Release: 2.0.48 | Release Date: March 2, 2026

# SQLAlchemy 2.0 Documentation

# PostgreSQL

Support for the PostgreSQL database.

The following table summarizes current support levels for database release versions.

Supported PostgreSQL versions
Support type | Versions
--- | ---
Supported version | 9.6+
Best effort | 9+

## DBAPI Support

The following dialect/DBAPI options are available. Please refer to individual DBAPI sections for connect information.

- psycopg2

- psycopg (a.k.a. psycopg 3)

- pg8000

- asyncpg

- psycopg2cffi

## Sequences/SERIAL/IDENTITY

PostgreSQL supports sequences, and SQLAlchemy uses these as the default means of creating new primary key values for integer-based primary key columns. When creating tables, SQLAlchemy will issue the `SERIAL` datatype for integer-based primary key columns, which generates a sequence and server side default corresponding to the column.

To specify a specific named sequence to be used for primary key generation, use the `Sequence()` construct:

    Table(
        "sometable",
        metadata,
        Column(
            "id", Integer, Sequence("some_id_seq", start=1), primary_key=True
        ),
    )

When SQLAlchemy issues a single INSERT statement, to fulfill the contract of having the “last insert identifier” available, a RETURNING clause is added to the INSERT statement which specifies the primary key columns should be returned after the statement completes. The RETURNING functionality only takes place if PostgreSQL 8.2 or later is in use. As a fallback approach, the sequence, whether specified explicitly or implicitly via `SERIAL`, is executed independently beforehand, the returned value to be used in the subsequent insert. Note that when an `insert()` construct is executed using “executemany” semantics, the “last inserted identifier” functionality does not apply; no RETURNING clause is emitted nor is the sequence pre-executed in this case.

### PostgreSQL 10 and above IDENTITY columns

PostgreSQL 10 and above have a new IDENTITY feature that supersedes the use of SERIAL. The `Identity` construct in a `Column` can be used to control its behavior:

    from sqlalchemy import Table, Column, MetaData, Integer, Computed

    metadata = MetaData()

    data = Table(
        "data",
        metadata,
        Column(
            "id", Integer, Identity(start=42, cycle=True), primary_key=True
        ),
        Column("data", String),
    )

The CREATE TABLE for the above `Table` object would be:

    CREATE TABLE data (
        id INTEGER GENERATED BY DEFAULT AS IDENTITY (START WITH 42 CYCLE),
        data VARCHAR,
        PRIMARY KEY (id)
    )

Changed in version 1.4: Added `Identity` construct in a `Column` to specify the option of an autoincrementing column.

Note

Previous versions of SQLAlchemy did not have built-in support for rendering of IDENTITY, and could use the following compilation hook to replace occurrences of SERIAL with IDENTITY:

    from sqlalchemy.schema import CreateColumn
    from sqlalchemy.ext.compiler import compiles

    @compiles(CreateColumn, "postgresql")
    def use_identity(element, compiler, **kw):
        text = compiler.visit_create_column(element, **kw)
        text = text.replace("SERIAL", "INT GENERATED BY DEFAULT AS IDENTITY")
        return text

Using the above, a table such as:

    t = Table(
        "t", m, Column("id", Integer, primary_key=True), Column("data", String)
    )

Will generate on the backing database as:

    CREATE TABLE t (
        id INT GENERATED BY DEFAULT AS IDENTITY,
        data VARCHAR,
        PRIMARY KEY (id)
    )

## Server Side Cursors

Server-side cursor support is available for the psycopg2, asyncpg dialects and may also be available in others.

Server side cursors are enabled on a per-statement basis by using the `Connection.execution_options.stream_results` connection execution option:

    with engine.connect() as conn:
        result = conn.execution_options(stream_results=True).execute(
            text("select * from table")
        )

Note that some kinds of SQL statements may not be supported with server side cursors; generally, only SQL statements that return rows should be used with this option.

Deprecated since version 1.4: The dialect-level server_side_cursors flag is deprecated and will be removed in a future release. Please use the `Connection.stream_results` execution option for unbuffered cursor support.

See also

Using Server Side Cursors (a.k.a. stream results)

## Transaction Isolation Level

Most SQLAlchemy dialects support setting of transaction isolation level using the `create_engine.isolation_level` parameter at the `create_engine()` level, and at the `Connection` level via the `Connection.execution_options.isolation_level` parameter.

For PostgreSQL dialects, this feature works either by making use of the DBAPI-specific features, such as psycopg2’s isolation level flags which will embed the isolation level setting inline with the `"BEGIN"` statement, or for DBAPIs with no direct support by emitting `SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL <level>` ahead of the `"BEGIN"` statement emitted by the DBAPI. For the special AUTOCOMMIT isolation level, DBAPI-specific techniques are used which is typically an `.autocommit` flag on the DBAPI connection object.

To set isolation level using `create_engine()`:

    engine = create_engine(
        "postgresql+pg8000://scott:tiger@localhost/test",
        isolation_level="REPEATABLE READ",
    )

To set using per-connection execution options:

    with engine.connect() as conn:
        conn = conn.execution_options(isolation_level="REPEATABLE READ")
        with conn.begin():
            ...  # work with transaction

There are also more options for isolation level configurations, such as “sub-engine” objects linked to a main `Engine` which each apply different isolation level settings. See the discussion at Setting Transaction Isolation Levels including DBAPI Autocommit for background.

Valid values for `isolation_level` on most PostgreSQL dialects include:

- `READ COMMITTED`

- `READ UNCOMMITTED`

- `REPEATABLE READ`

- `SERIALIZABLE`

- `AUTOCOMMIT`

See also

Setting Transaction Isolation Levels including DBAPI Autocommit

Setting READ ONLY / DEFERRABLE

Psycopg2 Transaction Isolation Level

pg8000 Transaction Isolation Level

## Setting READ ONLY / DEFERRABLE

Most PostgreSQL dialects support setting the “READ ONLY” and “DEFERRABLE” characteristics of the transaction, which is in addition to the isolation level setting. These two attributes can be established either in conjunction with or independently of the isolation level by passing the `postgresql_readonly` and `postgresql_deferrable` flags with `Connection.execution_options()`. The example below illustrates passing the `"SERIALIZABLE"` isolation level at the same time as setting “READ ONLY” and “DEFERRABLE”:

    with engine.connect() as conn:
        conn = conn.execution_options(
            isolation_level="SERIALIZABLE",
            postgresql_readonly=True,
            postgresql_deferrable=True,
        )
        with conn.begin():
            ...  # work with transaction

Note that some DBAPIs such as asyncpg only support “readonly” with SERIALIZABLE isolation.

Added in version 1.4: added support for the `postgresql_readonly` and `postgresql_deferrable` execution options.

## Temporary Table / Resource Reset for Connection Pooling

The `QueuePool` connection pool implementation used by the SQLAlchemy `Engine` object includes reset on return behavior that will invoke the DBAPI `.rollback()` method when connections are returned to the pool. While this rollback will clear out the immediate state used by the previous transaction, it does not cover a wider range of session-level state, including temporary tables as well as other server state such as prepared statement handles and statement caches. The PostgreSQL database includes a variety of commands which may be used to reset this state, including `DISCARD`, `RESET`, `DEALLOCATE`, and `UNLISTEN`.

To install one or more of these commands as the means of performing reset-on-return, the `PoolEvents.reset()` event hook may be used, as demonstrated in the example below. The implementation will end transactions in progress as well as discard temporary tables using the `CLOSE`, `RESET` and `DISCARD` commands; see the PostgreSQL documentation for background on what each of these statements do.

The `create_engine.pool_reset_on_return` parameter is set to `None` so that the custom scheme can replace the default behavior completely. The custom hook implementation calls `.rollback()` in any case, as it’s usually important that the DBAPI’s own tracking of commit/rollback will remain consistent with the state of the transaction:

    from sqlalchemy import create_engine
    from sqlalchemy import event

    postgresql_engine = create_engine(
        "postgresql+psycopg2://scott:tiger@hostname/dbname",
        # disable default reset-on-return scheme
        pool_reset_on_return=None,
    )

    @event.listens_for(postgresql_engine, "reset")
    def _reset_postgresql(dbapi_connection, connection_record, reset_state):
        if not reset_state.terminate_only:
            dbapi_connection.execute("CLOSE ALL")
            dbapi_connection.execute("RESET ALL")
            dbapi_connection.execute("DISCARD TEMP")

        # so that the DBAPI itself knows that the connection has been
        # reset
        dbapi_connection.rollback()

Changed in version 2.0.0b3: Added additional state arguments to the `PoolEvents.reset()` event and additionally ensured the event is invoked for all “reset” occurrences, so that it’s appropriate as a place for custom “reset” handlers. Previous schemes which use the `PoolEvents.checkin()` handler remain usable as well.

See also

Reset On Return - in the Connection Pooling documentation

## Setting Alternate Search Paths on Connect

The PostgreSQL `search_path` variable refers to the list of schema names that will be implicitly referenced when a particular table or other object is referenced in a SQL statement. As detailed in the next section Remote-Schema Table Introspection and PostgreSQL search_path, SQLAlchemy is generally organized around the concept of keeping this variable at its default value of `public`, however, in order to have it set to any arbitrary name or names when connections are used automatically, the “SET SESSION search_path” command may be invoked for all connections in a pool using the following event handler, as discussed at Setting a Default Schema for New Connections:

    from sqlalchemy import event
    from sqlalchemy import create_engine

    engine = create_engine("postgresql+psycopg2://scott:tiger@host/dbname")

    @event.listens_for(engine, "connect", insert=True)
    def set_search_path(dbapi_connection, connection_record):
        existing_autocommit = dbapi_connection.autocommit
        dbapi_connection.autocommit = True
        cursor = dbapi_connection.cursor()
        cursor.execute("SET SESSION search_path='%s'" % schema_name)
        cursor.close()
        dbapi_connection.autocommit = existing_autocommit

The reason the recipe is complicated by use of the `.autocommit` DBAPI attribute is so that when the `SET SESSION search_path` directive is invoked, it is invoked outside of the scope of any transaction and therefore will not be reverted when the DBAPI connection has a rollback.

See also

Setting a Default Schema for New Connections - in the Describing Databases with MetaData documentation

## Remote-Schema Table Introspection and PostgreSQL search_path

Section Best Practices Summarized

keep the `search_path` variable set to its default of `public`, without any other schema names. Ensure the username used to connect does not match remote schemas, or ensure the `"$user"` token is removed from `search_path`. For other schema names, name these explicitly within `Table` definitions. Alternatively, the `postgresql_ignore_search_path` option will cause all reflected `Table` objects to have a `Table.schema` attribute set up.

The PostgreSQL dialect can reflect tables from any schema, as outlined in Reflecting Tables from Other Schemas.

In all cases, the first thing SQLAlchemy does when reflecting tables is to determine the default schema for the current database connection. It does this using the PostgreSQL `current_schema()` function, illustated below using a PostgreSQL client session (i.e. using the `psql` tool):

    test=> select current_schema();
    current_schema
    ----------------
    public
    (1 row)

Above we see that on a plain install of PostgreSQL, the default schema name is the name `public`.

However, if your database username matches the name of a schema, PostgreSQL’s default is to then use that name as the default schema. Below, we log in using the username `scott`. When we create a schema named `scott`, it implicitly changes the default schema:

    test=> select current_schema();
    current_schema
    ----------------
    public
    (1 row)

    test=> create schema scott;
    CREATE SCHEMA
    test=> select current_schema();
    current_schema
    ----------------
    scott
    (1 row)

The behavior of `current_schema()` is derived from the PostgreSQL search path variable `search_path`, which in modern PostgreSQL versions defaults to this:

    test=> show search_path;
    search_path
    -----------------
    "$user", public
    (1 row)

Where above, the `"$user"` variable will inject the current username as the default schema, if one exists. Otherwise, `public` is used.

When a `Table` object is reflected, if it is present in the schema indicated by the `current_schema()` function, the schema name assigned to the “.schema” attribute of the Table is the Python “None” value. Otherwise, the “.schema” attribute will be assigned the string name of that schema.

With regards to tables which these `Table` objects refer to via foreign key constraint, a decision must be made as to how the `.schema` is represented in those remote tables, in the case where that remote schema name is also a member of the current `search_path`.

By default, the PostgreSQL dialect mimics the behavior encouraged by PostgreSQL’s own `pg_get_constraintdef()` builtin procedure. This function returns a sample definition for a particular foreign key constraint, omitting the referenced schema name from that definition when the name is also in the PostgreSQL schema search path. The interaction below illustrates this behavior:

    test=> CREATE TABLE test_schema.referred(id INTEGER PRIMARY KEY);
    CREATE TABLE
    test=> CREATE TABLE referring(
    test(>         id INTEGER PRIMARY KEY,
    test(>         referred_id INTEGER REFERENCES test_schema.referred(id));
    CREATE TABLE
    test=> SET search_path TO public, test_schema;
    test=> SELECT pg_catalog.pg_get_constraintdef(r.oid, true) FROM
    test-> pg_catalog.pg_class c JOIN pg_catalog.pg_namespace n
    test-> ON n.oid = c.relnamespace
    test-> JOIN pg_catalog.pg_constraint r  ON c.oid = r.conrelid
    test-> WHERE c.relname='referring' AND r.contype = 'f'
    test-> ;
                   pg_get_constraintdef
    ---------------------------------------------------
     FOREIGN KEY (referred_id) REFERENCES referred(id)
    (1 row)

Above, we created a table `referred` as a member of the remote schema `test_schema`, however when we added `test_schema` to the PG `search_path` and then asked `pg_get_constraintdef()` for the `FOREIGN KEY` syntax, `test_schema` was not included in the output of the function.

On the other hand, if we set the search path back to the typical default of `public`:

    test=> SET search_path TO public;
    SET

The same query against `pg_get_constraintdef()` now returns the fully schema-qualified name for us:

    test=> SELECT pg_catalog.pg_get_constraintdef(r.oid, true) FROM
    test-> pg_catalog.pg_class c JOIN pg_catalog.pg_namespace n
    test-> ON n.oid = c.relnamespace
    test-> JOIN pg_catalog.pg_constraint r  ON c.oid = r.conrelid
    test-> WHERE c.relname='referring' AND r.contype = 'f';
                         pg_get_constraintdef
    ---------------------------------------------------------------
     FOREIGN KEY (referred_id) REFERENCES test_schema.referred(id)
    (1 row)

SQLAlchemy will by default use the return value of `pg_get_constraintdef()` in order to determine the remote schema name. That is, if our `search_path` were set to include `test_schema`, and we invoked a table reflection process as follows:

    >>> from sqlalchemy import Table, MetaData, create_engine, text
    >>> engine = create_engine("postgresql+psycopg2://scott:tiger@localhost/test")
    >>> with engine.connect() as conn:
    ...     conn.execute(text("SET search_path TO test_schema, public"))
    ...     metadata_obj = MetaData()
    ...     referring = Table("referring", metadata_obj, autoload_with=conn)
    <sqlalchemy.engine.result.CursorResult object at 0x101612ed0>

The above process would deliver to the `MetaData.tables` collection `referred` table named without the schema:

    >>> metadata_obj.tables["referred"].schema is None
    True

To alter the behavior of reflection such that the referred schema is maintained regardless of the `search_path` setting, use the `postgresql_ignore_search_path` option, which can be specified as a dialect-specific argument to both `Table` as well as `MetaData.reflect()`:

    >>> with engine.connect() as conn:
    ...     conn.execute(text("SET search_path TO test_schema, public"))
    ...     metadata_obj = MetaData()
    ...     referring = Table(
    ...         "referring",
    ...         metadata_obj,
    ...         autoload_with=conn,
    ...         postgresql_ignore_search_path=True,
    ...     )
    <sqlalchemy.engine.result.CursorResult object at 0x1016126d0>

We will now have `test_schema.referred` stored as schema-qualified:

    >>> metadata_obj.tables["test_schema.referred"].schema
    'test_schema'

See also

Interaction of Schema-qualified Reflection with the Default Schema - discussion of the issue from a backend-agnostic perspective

The Schema Search Path - on the PostgreSQL website.

## INSERT/UPDATE…RETURNING

The dialect supports PG 8.2’s `INSERT..RETURNING`, `UPDATE..RETURNING` and `DELETE..RETURNING` syntaxes. `INSERT..RETURNING` is used by default for single-row INSERT statements in order to fetch newly generated primary key identifiers. To specify an explicit `RETURNING` clause, use the `_UpdateBase.returning()` method on a per-statement basis:

    # INSERT..RETURNING
    result = (
        table.insert().returning(table.c.col1, table.c.col2).values(name="foo")
    )
    print(result.fetchall())

    # UPDATE..RETURNING
    result = (
        table.update()
        .returning(table.c.col1, table.c.col2)
        .where(table.c.name == "foo")
        .values(name="bar")
    )
    print(result.fetchall())

    # DELETE..RETURNING
    result = (
        table.delete()
        .returning(table.c.col1, table.c.col2)
        .where(table.c.name == "foo")
    )
    print(result.fetchall())

## INSERT…ON CONFLICT (Upsert)

Starting with version 9.5, PostgreSQL allows “upserts” (update or insert) of rows into a table via the `ON CONFLICT` clause of the `INSERT` statement. A candidate row will only be inserted if that row does not violate any unique constraints. In the case of a unique constraint violation, a secondary action can occur which can be either “DO UPDATE”, indicating that the data in the target row should be updated, or “DO NOTHING”, which indicates to silently skip this row.

Conflicts are determined using existing unique constraints and indexes. These constraints may be identified either using their name as stated in DDL, or they may be inferred by stating the columns and conditions that comprise the indexes.

SQLAlchemy provides `ON CONFLICT` support via the PostgreSQL-specific `insert()` function, which provides the generative methods `Insert.on_conflict_do_update()` and `Insert.on_conflict_do_nothing()`:

    >>> from sqlalchemy.dialects.postgresql import insert
    >>> insert_stmt = insert(my_table).values(
    ...     id="some_existing_id", data="inserted value"
    ... )
    >>> do_nothing_stmt = insert_stmt.on_conflict_do_nothing(index_elements=["id"])
    >>> print(do_nothing_stmt)
    INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
    ON CONFLICT (id) DO NOTHING
    >>> do_update_stmt = insert_stmt.on_conflict_do_update(
    ...     constraint="pk_my_table", set_=dict(data="updated value")
    ... )
    >>> print(do_update_stmt)
    INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
    ON CONFLICT ON CONSTRAINT pk_my_table DO UPDATE SET data = %(param_1)s

See also

INSERT .. ON CONFLICT - in the PostgreSQL documentation.

### Specifying the Target

Both methods supply the “target” of the conflict using either the named constraint or by column inference:

- The `Insert.on_conflict_do_update.index_elements` argument specifies a sequence containing string column names, `Column` objects, and/or SQL expression elements, which would identify a unique index:

      >>> do_update_stmt = insert_stmt.on_conflict_do_update(
      ...     index_elements=["id"], set_=dict(data="updated value")
      ... )
      >>> print(do_update_stmt)
      INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
      ON CONFLICT (id) DO UPDATE SET data = %(param_1)s
      >>> do_update_stmt = insert_stmt.on_conflict_do_update(
      ...     index_elements=[my_table.c.id], set_=dict(data="updated value")
      ... )
      >>> print(do_update_stmt)
      INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
      ON CONFLICT (id) DO UPDATE SET data = %(param_1)s

- When using `Insert.on_conflict_do_update.index_elements` to infer an index, a partial index can be inferred by also specifying the use the `Insert.on_conflict_do_update.index_where` parameter:

      >>> stmt = insert(my_table).values(user_email="a@b.com", data="inserted data")
      >>> stmt = stmt.on_conflict_do_update(
      ...     index_elements=[my_table.c.user_email],
      ...     index_where=my_table.c.user_email.like("%@gmail.com"),
      ...     set_=dict(data=stmt.excluded.data),
      ... )
      >>> print(stmt)
      INSERT INTO my_table (data, user_email)
      VALUES (%(data)s, %(user_email)s) ON CONFLICT (user_email)
      WHERE user_email LIKE %(user_email_1)s DO UPDATE SET data = excluded.data

- The `Insert.on_conflict_do_update.constraint` argument is used to specify an index directly rather than inferring it. This can be the name of a UNIQUE constraint, a PRIMARY KEY constraint, or an INDEX:

      >>> do_update_stmt = insert_stmt.on_conflict_do_update(
      ...     constraint="my_table_idx_1", set_=dict(data="updated value")
      ... )
      >>> print(do_update_stmt)
      INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
      ON CONFLICT ON CONSTRAINT my_table_idx_1 DO UPDATE SET data = %(param_1)s
      >>> do_update_stmt = insert_stmt.on_conflict_do_update(
      ...     constraint="my_table_pk", set_=dict(data="updated value")
      ... )
      >>> print(do_update_stmt)
      INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
      ON CONFLICT ON CONSTRAINT my_table_pk DO UPDATE SET data = %(param_1)s

- The `Insert.on_conflict_do_update.constraint` argument may also refer to a SQLAlchemy construct representing a constraint, e.g. `UniqueConstraint`, `PrimaryKeyConstraint`, `Index`, or `ExcludeConstraint`. In this use, if the constraint has a name, it is used directly. Otherwise, if the constraint is unnamed, then inference will be used, where the expressions and optional WHERE clause of the constraint will be spelled out in the construct. This use is especially convenient to refer to the named or unnamed primary key of a `Table` using the `Table.primary_key` attribute:

      >>> do_update_stmt = insert_stmt.on_conflict_do_update(
      ...     constraint=my_table.primary_key, set_=dict(data="updated value")
      ... )
      >>> print(do_update_stmt)
      INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
      ON CONFLICT (id) DO UPDATE SET data = %(param_1)s

### The SET Clause

`ON CONFLICT...DO UPDATE` is used to perform an update of the already existing row, using any combination of new values as well as values from the proposed insertion. These values are specified using the `Insert.on_conflict_do_update.set_` parameter. This parameter accepts a dictionary which consists of direct values for UPDATE:

    >>> stmt = insert(my_table).values(id="some_id", data="inserted value")
    >>> do_update_stmt = stmt.on_conflict_do_update(
    ...     index_elements=["id"], set_=dict(data="updated value")
    ... )
    >>> print(do_update_stmt)
    INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
    ON CONFLICT (id) DO UPDATE SET data = %(param_1)s

Warning

The `Insert.on_conflict_do_update()` method does not take into account Python-side default UPDATE values or generation functions, e.g. those specified using `Column.onupdate`. These values will not be exercised for an ON CONFLICT style of UPDATE, unless they are manually specified in the `Insert.on_conflict_do_update.set_` dictionary.

### Updating using the Excluded INSERT Values

In order to refer to the proposed insertion row, the special alias `Insert.excluded` is available as an attribute on the `Insert` object; this object is a `ColumnCollection` which alias contains all columns of the target table:

    >>> stmt = insert(my_table).values(
    ...     id="some_id", data="inserted value", author="jlh"
    ... )
    >>> do_update_stmt = stmt.on_conflict_do_update(
    ...     index_elements=["id"],
    ...     set_=dict(data="updated value", author=stmt.excluded.author),
    ... )
    >>> print(do_update_stmt)
    INSERT INTO my_table (id, data, author)
    VALUES (%(id)s, %(data)s, %(author)s)
    ON CONFLICT (id) DO UPDATE SET data = %(param_1)s, author = excluded.author

### Additional WHERE Criteria

The `Insert.on_conflict_do_update()` method also accepts a WHERE clause using the `Insert.on_conflict_do_update.where` parameter, which will limit those rows which receive an UPDATE:

    >>> stmt = insert(my_table).values(
    ...     id="some_id", data="inserted value", author="jlh"
    ... )
    >>> on_update_stmt = stmt.on_conflict_do_update(
    ...     index_elements=["id"],
    ...     set_=dict(data="updated value", author=stmt.excluded.author),
    ...     where=(my_table.c.status == 2),
    ... )
    >>> print(on_update_stmt)
    INSERT INTO my_table (id, data, author)
    VALUES (%(id)s, %(data)s, %(author)s)
    ON CONFLICT (id) DO UPDATE SET data = %(param_1)s, author = excluded.author
    WHERE my_table.status = %(status_1)s

### Skipping Rows with DO NOTHING

`ON CONFLICT` may be used to skip inserting a row entirely if any conflict with a unique or exclusion constraint occurs; below this is illustrated using the `Insert.on_conflict_do_nothing()` method:

    >>> stmt = insert(my_table).values(id="some_id", data="inserted value")
    >>> stmt = stmt.on_conflict_do_nothing(index_elements=["id"])
    >>> print(stmt)
    INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
    ON CONFLICT (id) DO NOTHING

If `DO NOTHING` is used without specifying any columns or constraint, it has the effect of skipping the INSERT for any unique or exclusion constraint violation which occurs:

    >>> stmt = insert(my_table).values(id="some_id", data="inserted value")
    >>> stmt = stmt.on_conflict_do_nothing()
    >>> print(stmt)
    INSERT INTO my_table (id, data) VALUES (%(id)s, %(data)s)
    ON CONFLICT DO NOTHING

## Full Text Search

PostgreSQL’s full text search system is available through the use of the `func` namespace, combined with the use of custom operators via the `Operators.bool_op()` method. For simple cases with some degree of cross-backend compatibility, the `Operators.match()` operator may also be used.

### Simple plain text matching with `match()`

The `Operators.match()` operator provides for cross-compatible simple text matching. For the PostgreSQL backend, it’s hardcoded to generate an expression using the `@@` operator in conjunction with the `plainto_tsquery()` PostgreSQL function.

On the PostgreSQL dialect, an expression like the following:

    select(sometable.c.text.match("search string"))

would emit to the database:

    SELECT text @@ plainto_tsquery('search string') FROM table

Above, passing a plain string to `Operators.match()` will automatically make use of `plainto_tsquery()` to specify the type of tsquery. This establishes basic database cross-compatibility for `Operators.match()` with other backends.

Changed in version 2.0: The default tsquery generation function used by the PostgreSQL dialect with `Operators.match()` is `plainto_tsquery()`.

To render exactly what was rendered in 1.4, use the following form:

    from sqlalchemy import func

    select(sometable.c.text.bool_op("@@")(func.to_tsquery("search string")))

Which would emit:

    SELECT text @@ to_tsquery('search string') FROM table

### Using PostgreSQL full text functions and operators directly

Text search operations beyond the simple use of `Operators.match()` may make use of the `func` namespace to generate PostgreSQL full-text functions, in combination with `Operators.bool_op()` to generate any boolean operator.

For example, the query:

    select(func.to_tsquery("cat").bool_op("@>")(func.to_tsquery("cat & rat")))

would generate:

    SELECT to_tsquery('cat') @> to_tsquery('cat & rat')

The `TSVECTOR` type can provide for explicit CAST:

    from sqlalchemy.dialects.postgresql import TSVECTOR
    from sqlalchemy import select, cast

    select(cast("some text", TSVECTOR))

produces a statement equivalent to:

    SELECT CAST('some text' AS TSVECTOR) AS anon_1

The `func` namespace is augmented by the PostgreSQL dialect to set up correct argument and return types for most full text search functions. These functions are used automatically by the `sqlalchemy.sql.expression.func` namespace assuming the `sqlalchemy.dialects.postgresql` package has been imported, or `create_engine()` has been invoked using a `postgresql` dialect. These functions are documented at:

- `to_tsvector`

- `to_tsquery`

- `plainto_tsquery`

- `phraseto_tsquery`

- `websearch_to_tsquery`

- `ts_headline`

### Specifying the “regconfig” with `match()` or custom operators

PostgreSQL’s `plainto_tsquery()` function accepts an optional “regconfig” argument that is used to instruct PostgreSQL to use a particular pre-computed GIN or GiST index in order to perform the search. When using `Operators.match()`, this additional parameter may be specified using the `postgresql_regconfig` parameter, such as:

    select(mytable.c.id).where(
        mytable.c.title.match("somestring", postgresql_regconfig="english")
    )

Which would emit:

    SELECT mytable.id FROM mytable
    WHERE mytable.title @@ plainto_tsquery('english', 'somestring')

When using other PostgreSQL search functions with `func`, the “regconfig” parameter may be passed directly as the initial argument:

    select(mytable.c.id).where(
        func.to_tsvector("english", mytable.c.title).bool_op("@@")(
            func.to_tsquery("english", "somestring")
        )
    )

produces a statement equivalent to:

    SELECT mytable.id FROM mytable
    WHERE to_tsvector('english', mytable.title) @@
        to_tsquery('english', 'somestring')

It is recommended that you use the `EXPLAIN ANALYZE...` tool from PostgreSQL to ensure that you are generating queries with SQLAlchemy that take full advantage of any indexes you may have created for full text search.

See also

Full Text Search - in the PostgreSQL documentation

## FROM ONLY …

The dialect supports PostgreSQL’s ONLY keyword for targeting only a particular table in an inheritance hierarchy. This can be used to produce the `SELECT ... FROM ONLY`, `UPDATE ONLY ...`, and `DELETE FROM ONLY ...` syntaxes. It uses SQLAlchemy’s hints mechanism:

    # SELECT ... FROM ONLY ...
    result = table.select().with_hint(table, "ONLY", "postgresql")
    print(result.fetchall())

    # UPDATE ONLY ...
    table.update(values=dict(foo="bar")).with_hint(
        "ONLY", dialect_name="postgresql"
    )

    # DELETE FROM ONLY ...
    table.delete().with_hint("ONLY", dialect_name="postgresql")

## PostgreSQL-Specific Index Options

Several extensions to the `Index` construct are available, specific to the PostgreSQL dialect.

### Covering Indexes

A covering index includes additional columns that are not part of the index key but are stored in the index, allowing PostgreSQL to satisfy queries using only the index without accessing the table (an “index-only scan”). This is indicated on the index using the `INCLUDE` clause. The `postgresql_include` option for `Index` (as well as `UniqueConstraint`) renders `INCLUDE(colname)` for the given string names:

    Index("my_index", table.c.x, postgresql_include=["y"])

would render the index as `CREATE INDEX my_index ON table (x) INCLUDE (y)`

Note that this feature requires PostgreSQL 11 or later.

See also

INCLUDE - the same feature implemented for `UniqueConstraint`

Added in version 1.4: - support for covering indexes with `Index`. support for `UniqueConstraint` was in 2.0.41

### Partial Indexes

Partial indexes add criterion to the index definition so that the index is applied to a subset of rows. These can be specified on `Index` using the `postgresql_where` keyword argument:

    Index("my_index", my_table.c.id, postgresql_where=my_table.c.value > 10)

### Operator Classes

PostgreSQL allows the specification of an operator class for each column of an index (see https://www.postgresql.org/docs/current/interactive/indexes-opclass.html). The `Index` construct allows these to be specified via the `postgresql_ops` keyword argument:

    Index(
        "my_index",
        my_table.c.id,
        my_table.c.data,
        postgresql_ops={"data": "text_pattern_ops", "id": "int4_ops"},
    )

Note that the keys in the `postgresql_ops` dictionaries are the “key” name of the `Column`, i.e. the name used to access it from the `.c` collection of `Table`, which can be configured to be different than the actual name of the column as expressed in the database.

If `postgresql_ops` is to be used against a complex SQL expression such as a function call, then to apply to the column it must be given a label that is identified in the dictionary by name, e.g.:

    Index(
        "my_index",
        my_table.c.id,
        func.lower(my_table.c.data).label("data_lower"),
        postgresql_ops={"data_lower": "text_pattern_ops", "id": "int4_ops"},
    )

Operator classes are also supported by the `ExcludeConstraint` construct using the `ExcludeConstraint.ops` parameter. See that parameter for details.

Added in version 1.3.21: added support for operator classes with `ExcludeConstraint`.

### Index Types

PostgreSQL provides several index types: B-Tree, Hash, GiST, and GIN, as well as the ability for users to create their own (see https://www.postgresql.org/docs/current/static/indexes-types.html). These can be specified on `Index` using the `postgresql_using` keyword argument:

    Index("my_index", my_table.c.data, postgresql_using="gin")

The value passed to the keyword argument will be simply passed through to the underlying CREATE INDEX command, so it must be a valid index type for your version of PostgreSQL.

### Index Storage Parameters

PostgreSQL allows storage parameters to be set on indexes. The storage parameters available depend on the index method used by the index. Storage parameters can be specified on `Index` using the `postgresql_with` keyword argument:

    Index("my_index", my_table.c.data, postgresql_with={"fillfactor": 50})

PostgreSQL allows to define the tablespace in which to create the index. The tablespace can be specified on `Index` using the `postgresql_tablespace` keyword argument:

    Index("my_index", my_table.c.data, postgresql_tablespace="my_tablespace")

Note that the same option is available on `Table` as well.

### Indexes with CONCURRENTLY

The PostgreSQL index option CONCURRENTLY is supported by passing the flag `postgresql_concurrently` to the `Index` construct:

    tbl = Table("testtbl", m, Column("data", Integer))

    idx1 = Index("test_idx1", tbl.c.data, postgresql_concurrently=True)

The above index construct will render DDL for CREATE INDEX, assuming PostgreSQL 8.2 or higher is detected or for a connection-less dialect, as:

    CREATE INDEX CONCURRENTLY test_idx1 ON testtbl (data)

For DROP INDEX, assuming PostgreSQL 9.2 or higher is detected or for a connection-less dialect, it will emit:

    DROP INDEX CONCURRENTLY test_idx1

When using CONCURRENTLY, the PostgreSQL database requires that the statement be invoked outside of a transaction block. The Python DBAPI enforces that even for a single statement, a transaction is present, so to use this construct, the DBAPI’s “autocommit” mode must be used:

    metadata = MetaData()
    table = Table("foo", metadata, Column("id", String))
    index = Index("foo_idx", table.c.id, postgresql_concurrently=True)

    with engine.connect() as conn:
        with conn.execution_options(isolation_level="AUTOCOMMIT"):
            table.create(conn)

See also

Transaction Isolation Level

## PostgreSQL Index Reflection

The PostgreSQL database creates a UNIQUE INDEX implicitly whenever the UNIQUE CONSTRAINT construct is used. When inspecting a table using `Inspector`, the `Inspector.get_indexes()` and the `Inspector.get_unique_constraints()` will report on these two constructs distinctly; in the case of the index, the key `duplicates_constraint` will be present in the index entry if it is detected as mirroring a constraint. When performing reflection using `Table(..., autoload_with=engine)`, the UNIQUE INDEX is not returned in `Table.indexes` when it is detected as mirroring a `UniqueConstraint` in the `Table.constraints` collection .

## Special Reflection Options

The `Inspector` used for the PostgreSQL backend is an instance of `PGInspector`, which offers additional methods:

    from sqlalchemy import create_engine, inspect

    engine = create_engine("postgresql+psycopg2://localhost/test")
    insp = inspect(engine)  # will be a PGInspector

    print(insp.get_enums())

Object Name | Description
--- | ---
PGInspector |

class sqlalchemy.dialects.postgresql.base.PGInspector

  inherits from `sqlalchemy.engine.reflection.Inspector`

  Member Name | Description
  --- | ---
  get_domains() | Return a list of DOMAIN objects.
  get_enums() | Return a list of ENUM objects.
  get_foreign_table_names() | Return a list of FOREIGN TABLE names.
  get_table_oid() | Return the OID for the given table name.
  has_type() | Return if the database has the specified type in the provided schema.

  method `sqlalchemy.dialects.postgresql.base.PGInspector.`get_domains(schema: str | None = None) → List[ReflectedDomain]

    Return a list of DOMAIN objects.

    Each member is a dictionary containing these fields:

    > - name - name of the domain

    > - schema - the schema name for the domain.

    > - visible - boolean, whether or not this domain is visible in the default search path.

    > - type - the type defined by this domain.

    > - nullable - Indicates if this domain can be `NULL`.

    > - default - The default value of the domain or `None` if the domain has no default.

    > - constraints - A list of dict with the constraint defined by this domain. Each element contains two keys: `name` of the constraint and `check` with the constraint text.

    Parameters:

      schema – schema name. If None, the default schema (typically ‘public’) is used. May also be set to `'*'` to indicate load domains for all schemas.

    Added in version 2.0.

  method `sqlalchemy.dialects.postgresql.base.PGInspector.`get_enums(schema: str | None = None) → List[ReflectedEnum]

    Return a list of ENUM objects.

    Each member is a dictionary containing these fields:

    > - name - name of the enum

    > - schema - the schema name for the enum.

    > - visible - boolean, whether or not this enum is visible in the default search path.

    > - labels - a list of string labels that apply to the enum.

    Parameters:

      schema – schema name. If None, the default schema (typically ‘public’) is used. May also be set to `'*'` to indicate load enums for all schemas.

  method `sqlalchemy.dialects.postgresql.base.PGInspector.`get_foreign_table_names(schema: str | None = None) → List[str]

    Return a list of FOREIGN TABLE names.

    Behavior is similar to that of `Inspector.get_table_names()`, except that the list is limited to those tables that report a `relkind` value of `f`.

  method `sqlalchemy.dialects.postgresql.base.PGInspector.`get_table_oid(table_name: str, schema: str | None = None) → int

    Return the OID for the given table name.

    Parameters:

      - table_name – string name of the table. For special quoting, use `quoted_name`.

      - schema – string schema name; if omitted, uses the default schema of the database connection. For special quoting, use `quoted_name`.

  method `sqlalchemy.dialects.postgresql.base.PGInspector.`has_type(type_name: str, schema: str | None = None, **kw: Any) → bool

    Return if the database has the specified type in the provided schema.

    Parameters:

      - type_name – the type to check.

      - schema – schema name. If None, the default schema (typically ‘public’) is used. May also be set to `'*'` to check in all schemas.

    Added in version 2.0.

## PostgreSQL Table Options

Several options for CREATE TABLE are supported directly by the PostgreSQL dialect in conjunction with the `Table` construct, listed in the following sections.

See also

PostgreSQL CREATE TABLE options - in the PostgreSQL documentation.

### `INHERITS`

Specifies one or more parent tables from which this table inherits columns and constraints, enabling table inheritance hierarchies in PostgreSQL.

    Table("some_table", metadata, ..., postgresql_inherits="some_supertable")

    Table("some_table", metadata, ..., postgresql_inherits=("t1", "t2", ...))

### `ON COMMIT`

Controls the behavior of temporary tables at transaction commit, with options to preserve rows, delete rows, or drop the table.

    Table("some_table", metadata, ..., postgresql_on_commit="PRESERVE ROWS")

### `PARTITION BY`

Declares the table as a partitioned table using the specified partitioning strategy (RANGE, LIST, or HASH) on the given column(s).

    Table(
        "some_table",
        metadata,
        ...,
        postgresql_partition_by="LIST (part_column)",
    )

### `TABLESPACE`

Specifies the tablespace where the table will be stored, allowing control over the physical location of table data on disk.

    Table("some_table", metadata, ..., postgresql_tablespace="some_tablespace")

The above option is also available on the `Index` construct.

### `USING`

Specifies the table access method to use for storing table data, such as `heap` (the default) or other custom access methods.

    Table("some_table", metadata, ..., postgresql_using="heap")

Added in version 2.0.26.

### `WITH OIDS`

Enables the legacy OID (object identifier) system column for the table, which assigns a unique identifier to each row.

    Table("some_table", metadata, ..., postgresql_with_oids=True)

### `WITHOUT OIDS`

Explicitly disables the OID system column for the table (the default behavior in modern PostgreSQL versions).

    Table("some_table", metadata, ..., postgresql_with_oids=False)

## PostgreSQL Constraint Options

The following sections indicate options which are supported by the PostgreSQL dialect in conjunction with selected constraint constructs.

### `NOT VALID`

Allows a constraint to be added without validating existing rows, improving performance when adding constraints to large tables. This option applies towards CHECK and FOREIGN KEY constraints when the constraint is being added to an existing table via ALTER TABLE, and has the effect that existing rows are not scanned during the ALTER operation against the constraint being added.

When using a SQL migration tool such as Alembic that renders ALTER TABLE constructs, the `postgresql_not_valid` argument may be specified as an additional keyword argument within the operation that creates the constraint, as in the following Alembic example:

    def update():
        op.create_foreign_key(
            "fk_user_address",
            "address",
            "user",
            ["user_id"],
            ["id"],
            postgresql_not_valid=True,
        )

The keyword is ultimately accepted directly by the `CheckConstraint`, `ForeignKeyConstraint` and `ForeignKey` constructs; when using a tool like Alembic, dialect-specific keyword arguments are passed through to these constructs from the migration operation directives:

    CheckConstraint("some_field IS NOT NULL", postgresql_not_valid=True)

    ForeignKeyConstraint(
        ["some_id"], ["some_table.some_id"], postgresql_not_valid=True
    )

Added in version 1.4.32.

See also

PostgreSQL ALTER TABLE options - in the PostgreSQL documentation.

### `INCLUDE`

This keyword is applicable to both a `UNIQUE` constraint as well as an `INDEX`. The `postgresql_include` option available for `UniqueConstraint` as well as `Index` creates a covering index by including additional columns in the underlying index without making them part of the key constraint. This option adds one or more columns as a “payload” to the index created automatically by PostgreSQL for the constraint. For example, the following table definition:

    Table(
        "mytable",
        metadata,
        Column("id", Integer, nullable=False),
        Column("value", Integer, nullable=False),
        UniqueConstraint("id", postgresql_include=["value"]),
    )

would produce the DDL statement

    CREATE TABLE mytable (
        id INTEGER NOT NULL,
        value INTEGER NOT NULL,
        UNIQUE (id) INCLUDE (value)
     )

Note that this feature requires PostgreSQL 11 or later.

Added in version 2.0.41: - added support for `postgresql_include` to `UniqueConstraint`, to complement the existing feature in `Index`.

See also

Covering Indexes - background on `postgresql_include` for the `Index` construct.

### Column list with foreign key `ON DELETE SET` actions

Allows selective column updates when a foreign key action is triggered, limiting which columns are set to NULL or DEFAULT upon deletion of a referenced row. This applies to `ForeignKey` and `ForeignKeyConstraint`, the `ForeignKey.ondelete` parameter will accept on the PostgreSQL backend only a string list of column names inside parenthesis, following the `SET NULL` or `SET DEFAULT` phrases, which will limit the set of columns that are subject to the action:

    fktable = Table(
        "fktable",
        metadata,
        Column("tid", Integer),
        Column("id", Integer),
        Column("fk_id_del_set_null", Integer),
        ForeignKeyConstraint(
            columns=["tid", "fk_id_del_set_null"],
            refcolumns=[pktable.c.tid, pktable.c.id],
            ondelete="SET NULL (fk_id_del_set_null)",
        ),
    )

Added in version 2.0.40.

## Table values, Table and Column valued functions, Row and Tuple objects

PostgreSQL makes great use of modern SQL forms such as table-valued functions, tables and rows as values. These constructs are commonly used as part of PostgreSQL’s support for complex datatypes such as JSON, ARRAY, and other datatypes. SQLAlchemy’s SQL expression language has native support for most table-valued and row-valued forms.

### Table-Valued Functions

Many PostgreSQL built-in functions are intended to be used in the FROM clause of a SELECT statement, and are capable of returning table rows or sets of table rows. A large portion of PostgreSQL’s JSON functions for example such as `json_array_elements()`, `json_object_keys()`, `json_each_text()`, `json_each()`, `json_to_record()`, `json_populate_recordset()` use such forms. These classes of SQL function calling forms in SQLAlchemy are available using the `FunctionElement.table_valued()` method in conjunction with `Function` objects generated from the `func` namespace.

Examples from PostgreSQL’s reference documentation follow below:

- `json_each()`:

      >>> from sqlalchemy import select, func
      >>> stmt = select(
      ...     func.json_each('{"a":"foo", "b":"bar"}').table_valued("key", "value")
      ... )
      >>> print(stmt)
      SELECT anon_1.key, anon_1.value
      FROM json_each(:json_each_1) AS anon_1

- `json_populate_record()`:

      >>> from sqlalchemy import select, func, literal_column
      >>> stmt = select(
      ...     func.json_populate_record(
      ...         literal_column("null::myrowtype"), '{"a":1,"b":2}'
      ...     ).table_valued("a", "b", name="x")
      ... )
      >>> print(stmt)
      SELECT x.a, x.b
      FROM json_populate_record(null::myrowtype, :json_populate_record_1) AS x

- `json_to_record()` - this form uses a PostgreSQL specific form of derived columns in the alias, where we may make use of `column()` elements with types to produce them. The `FunctionElement.table_valued()` method produces a `TableValuedAlias` construct, and the method `TableValuedAlias.render_derived()` method sets up the derived columns specification:

      >>> from sqlalchemy import select, func, column, Integer, Text
      >>> stmt = select(
      ...     func.json_to_record('{"a":1,"b":[1,2,3],"c":"bar"}')
      ...     .table_valued(
      ...         column("a", Integer),
      ...         column("b", Text),
      ...         column("d", Text),
      ...     )
      ...     .render_derived(name="x", with_types=True)
      ... )
      >>> print(stmt)
      SELECT x.a, x.b, x.d
      FROM json_to_record(:json_to_record_1) AS x(a INTEGER, b TEXT, d TEXT)

- `WITH ORDINALITY` - part of the SQL standard, `WITH ORDINALITY` adds an ordinal counter to the output of a function and is accepted by a limited set of PostgreSQL functions including `unnest()` and `generate_series()`. The `FunctionElement.table_valued()` method accepts a keyword parameter `with_ordinality` for this purpose, which accepts the string name that will be applied to the “ordinality” column:

      >>> from sqlalchemy import select, func
      >>> stmt = select(
      ...     func.generate_series(4, 1, -1)
      ...     .table_valued("value", with_ordinality="ordinality")
      ...     .render_derived()
      ... )
      >>> print(stmt)
      SELECT anon_1.value, anon_1.ordinality
      FROM generate_series(:generate_series_1, :generate_series_2, :generate_series_3)
      WITH ORDINALITY AS anon_1(value, ordinality)

Added in version 1.4.0b2.

See also

Table-Valued Functions - in the SQLAlchemy Unified Tutorial

### Column Valued Functions

Similar to the table valued function, a column valued function is present in the FROM clause, but delivers itself to the columns clause as a single scalar value. PostgreSQL functions such as `json_array_elements()`, `unnest()` and `generate_series()` may use this form. Column valued functions are available using the `FunctionElement.column_valued()` method of `FunctionElement`:

- `json_array_elements()`:

      >>> from sqlalchemy import select, func
      >>> stmt = select(
      ...     func.json_array_elements('["one", "two"]').column_valued("x")
      ... )
      >>> print(stmt)
      SELECT x
      FROM json_array_elements(:json_array_elements_1) AS x

- `unnest()` - in order to generate a PostgreSQL ARRAY literal, the `array()` construct may be used:

      >>> from sqlalchemy.dialects.postgresql import array
      >>> from sqlalchemy import select, func
      >>> stmt = select(func.unnest(array([1, 2])).column_valued())
      >>> print(stmt)
      SELECT anon_1
      FROM unnest(ARRAY[%(param_1)s, %(param_2)s]) AS anon_1

  The function can of course be used against an existing table-bound column that’s of type `ARRAY`:

      >>> from sqlalchemy import table, column, ARRAY, Integer
      >>> from sqlalchemy import select, func
      >>> t = table("t", column("value", ARRAY(Integer)))
      >>> stmt = select(func.unnest(t.c.value).column_valued("unnested_value"))
      >>> print(stmt)
      SELECT unnested_value
      FROM unnest(t.value) AS unnested_value

See also

Column Valued Functions - Table Valued Function as a Scalar Column - in the SQLAlchemy Unified Tutorial

### Row Types

Built-in support for rendering a `ROW` may be approximated using `func.ROW` with the `sqlalchemy.func` namespace, or by using the `tuple_()` construct:

    >>> from sqlalchemy import table, column, func, tuple_
    >>> t = table("t", column("id"), column("fk"))
    >>> stmt = (
    ...     t.select()
    ...     .where(tuple_(t.c.id, t.c.fk) > (1, 2))
    ...     .where(func.ROW(t.c.id, t.c.fk) < func.ROW(3, 7))
    ... )
    >>> print(stmt)
    SELECT t.id, t.fk
    FROM t
    WHERE (t.id, t.fk) > (:param_1, :param_2) AND ROW(t.id, t.fk) < ROW(:ROW_1, :ROW_2)

See also

PostgreSQL Row Constructors

PostgreSQL Row Constructor Comparison

### Table Types passed to Functions

PostgreSQL supports passing a table as an argument to a function, which is known as a “record” type. SQLAlchemy `FromClause` objects such as `Table` support this special form using the `FromClause.table_valued()` method, which is comparable to the `FunctionElement.table_valued()` method except that the collection of columns is already established by that of the `FromClause` itself:

    >>> from sqlalchemy import table, column, func, select
    >>> a = table("a", column("id"), column("x"), column("y"))
    >>> stmt = select(func.row_to_json(a.table_valued()))
    >>> print(stmt)
    SELECT row_to_json(a) AS row_to_json_1
    FROM a

Added in version 1.4.0b2.

## ARRAY Types

The PostgreSQL dialect supports arrays, both as multidimensional column types as well as array literals:

- `ARRAY` - ARRAY datatype

- `array` - array literal

- `array_agg()` - ARRAY_AGG SQL function

- `aggregate_order_by` - helper for PG’s ORDER BY aggregate function syntax.

## JSON Types

The PostgreSQL dialect supports both JSON and JSONB datatypes, including psycopg2’s native support and support for all of PostgreSQL’s special operators:

- `JSON`

- `JSONB`

- `JSONPATH`

## HSTORE Type

The PostgreSQL HSTORE type as well as hstore literals are supported:

- `HSTORE` - HSTORE datatype

- `hstore` - hstore literal

## ENUM Types

PostgreSQL has an independently creatable TYPE structure which is used to implement an enumerated type. This approach introduces significant complexity on the SQLAlchemy side in terms of when this type should be CREATED and DROPPED. The type object is also an independently reflectable entity. The following sections should be consulted:

- `ENUM` - DDL and typing support for ENUM.

- `PGInspector.get_enums()` - retrieve a listing of current ENUM types

- `ENUM.create()` , `ENUM.drop()` - individual CREATE and DROP commands for ENUM.

### Using ENUM with ARRAY

The combination of ENUM and ARRAY is not directly supported by backend DBAPIs at this time. Prior to SQLAlchemy 1.3.17, a special workaround was needed in order to allow this combination to work, described below.

Changed in version 1.3.17: The combination of ENUM and ARRAY is now directly handled by SQLAlchemy’s implementation without any workarounds needed.

    from sqlalchemy import TypeDecorator
    from sqlalchemy.dialects.postgresql import ARRAY

    class ArrayOfEnum(TypeDecorator):
        impl = ARRAY

        def bind_expression(self, bindvalue):
            return sa.cast(bindvalue, self)

        def result_processor(self, dialect, coltype):
            super_rp = super(ArrayOfEnum, self).result_processor(dialect, coltype)

            def handle_raw_string(value):
                inner = re.match(r"^{(.*)}$", value).group(1)
                return inner.split(",") if inner else []

            def process(value):
                if value is None:
                    return None
                return super_rp(handle_raw_string(value))

            return process

E.g.:

    Table(
        "mydata",
        metadata,
        Column("id", Integer, primary_key=True),
        Column("data", ArrayOfEnum(ENUM("a", "b", "c", name="myenum"))),
    )

This type is not included as a built-in type as it would be incompatible with a DBAPI that suddenly decides to support ARRAY of ENUM directly in a new version.

### Using JSON/JSONB with ARRAY

Similar to using ENUM, prior to SQLAlchemy 1.3.17, for an ARRAY of JSON/JSONB we need to render the appropriate CAST. Current psycopg2 drivers accommodate the result set correctly without any special steps.

Changed in version 1.3.17: The combination of JSON/JSONB and ARRAY is now directly handled by SQLAlchemy’s implementation without any workarounds needed.

    class CastingArray(ARRAY):
        def bind_expression(self, bindvalue):
            return sa.cast(bindvalue, self)

E.g.:

    Table(
        "mydata",
        metadata,
        Column("id", Integer, primary_key=True),
        Column("data", CastingArray(JSONB)),
    )

## Range and Multirange Types

PostgreSQL range and multirange types are supported for the psycopg, pg8000 and asyncpg dialects; the psycopg2 dialect supports the range types only.

Added in version 2.0.17: Added range and multirange support for the pg8000 dialect. pg8000 1.29.8 or greater is required.

Data values being passed to the database may be passed as string values or by using the `Range` data object.

Added in version 2.0: Added the backend-agnostic `Range` object used to indicate ranges. The `psycopg2`-specific range classes are no longer exposed and are only used internally by that particular dialect.

E.g. an example of a fully typed model using the `TSRANGE` datatype:

    from datetime import datetime

    from sqlalchemy.dialects.postgresql import Range
    from sqlalchemy.dialects.postgresql import TSRANGE
    from sqlalchemy.orm import DeclarativeBase
    from sqlalchemy.orm import Mapped
    from sqlalchemy.orm import mapped_column

    class Base(DeclarativeBase):
        pass

    class RoomBooking(Base):
        __tablename__ = "room_booking"

        id: Mapped[int] = mapped_column(primary_key=True)
        room: Mapped[str]
        during: Mapped[Range[datetime]] = mapped_column(TSRANGE)

To represent data for the `during` column above, the `Range` type is a simple dataclass that will represent the bounds of the range. Below illustrates an INSERT of a row into the above `room_booking` table:

    from sqlalchemy import create_engine
    from sqlalchemy.orm import Session

    engine = create_engine("postgresql+psycopg://scott:tiger@pg14/dbname")

    Base.metadata.create_all(engine)

    with Session(engine) as session:
        booking = RoomBooking(
            room="101", during=Range(datetime(2013, 3, 23), datetime(2013, 3, 25))
        )
        session.add(booking)
        session.commit()

Selecting from any range column will also return `Range` objects as indicated:

    from sqlalchemy import select

    with Session(engine) as session:
        for row in session.execute(select(RoomBooking.during)):
            print(row)

The available range datatypes are as follows:

- `INT4RANGE`

- `INT8RANGE`

- `NUMRANGE`

- `DATERANGE`

- `TSRANGE`

- `TSTZRANGE`

Object Name | Description
--- | ---
Range | Represent a PostgreSQL range.

class sqlalchemy.dialects.postgresql.Range

  inherits from `typing.Generic`

  Represent a PostgreSQL range.

  E.g.:

      r = Range(10, 50, bounds="()")

  The calling style is similar to that of psycopg and psycopg2, in part to allow easier migration from previous SQLAlchemy versions that used these objects directly.

  Parameters:

    - lower – Lower bound value, or None

    - upper – Upper bound value, or None

    - bounds – keyword-only, optional string value that is one of `"()"`, `"[)"`, `"(]"`, `"[]"`. Defaults to `"[)"`.

    - empty – keyword-only, optional bool indicating this is an “empty” range

  Added in version 2.0.

  Member Name | Description
  --- | ---
  __eq__() | Compare this range to the other taking into account bounds inclusivity, returning `True` if they are equal.
  adjacent_to() | Determine whether this range is adjacent to the other.
  contained_by() | Determine whether this range is a contained by other.
  contains() | Determine whether this range contains value.
  difference() | Compute the difference between this range and the other.
  intersection() | Compute the intersection of this range with the other.
  is_empty | A synonym for the ‘empty’ attribute.
  isempty | A synonym for the ‘empty’ attribute.
  lower | the lower bound
  lower_inc | Return True if the lower bound is inclusive.
  lower_inf | Return True if this range is non-empty and lower bound is infinite.
  not_extend_left_of() | Determine whether this does not extend to the left of other.
  not_extend_right_of() | Determine whether this does not extend to the right of other.
  overlaps() | Determine whether this range overlaps with other.
  strictly_left_of() | Determine whether this range is completely to the left of other.
  strictly_right_of() | Determine whether this range is completely to the right of other.
  union() | Compute the union of this range with the other.
  upper | the upper bound
  upper_inc | Return True if the upper bound is inclusive.
  upper_inf | Return True if this range is non-empty and the upper bound is infinite.

  method `sqlalchemy.dialects.postgresql.Range.`__eq__(other: Any) → bool

    Compare this range to the other taking into account bounds inclusivity, returning `True` if they are equal.

  method `sqlalchemy.dialects.postgresql.Range.`adjacent_to(other: Range[_T]) → bool

    Determine whether this range is adjacent to the other.

  method `sqlalchemy.dialects.postgresql.Range.`contained_by(other: Range[_T]) → bool

    Determine whether this range is a contained by other.

  method `sqlalchemy.dialects.postgresql.Range.`contains(value: _T | Range[_T]) → bool

    Determine whether this range contains value.

  method `sqlalchemy.dialects.postgresql.Range.`difference(other: Range[_T]) → Range[_T]

    Compute the difference between this range and the other.

    This raises a `ValueError` exception if the two ranges are “disjunct”, that is neither adjacent nor overlapping.

  method `sqlalchemy.dialects.postgresql.Range.`intersection(other: Range[_T]) → Range[_T]

    Compute the intersection of this range with the other.

    Added in version 2.0.10.

  attribute `sqlalchemy.dialects.postgresql.Range.`is_empty

    A synonym for the ‘empty’ attribute.

  attribute `sqlalchemy.dialects.postgresql.Range.`isempty

    A synonym for the ‘empty’ attribute.

  attribute `sqlalchemy.dialects.postgresql.Range.`lower: _T | None

    the lower bound

  attribute `sqlalchemy.dialects.postgresql.Range.`lower_inc

    Return True if the lower bound is inclusive.

  attribute `sqlalchemy.dialects.postgresql.Range.`lower_inf

    Return True if this range is non-empty and lower bound is infinite.

  method `sqlalchemy.dialects.postgresql.Range.`not_extend_left_of(other: Range[_T]) → bool

    Determine whether this does not extend to the left of other.

  method `sqlalchemy.dialects.postgresql.Range.`not_extend_right_of(other: Range[_T]) → bool

    Determine whether this does not extend to the right of other.

  method `sqlalchemy.dialects.postgresql.Range.`overlaps(other: Range[_T]) → bool

    Determine whether this range overlaps with other.

  method `sqlalchemy.dialects.postgresql.Range.`strictly_left_of(other: Range[_T]) → bool

    Determine whether this range is completely to the left of other.

  method `sqlalchemy.dialects.postgresql.Range.`strictly_right_of(other: Range[_T]) → bool

    Determine whether this range is completely to the right of other.

  method `sqlalchemy.dialects.postgresql.Range.`union(other: Range[_T]) → Range[_T]

    Compute the union of this range with the other.

    This raises a `ValueError` exception if the two ranges are “disjunct”, that is neither adjacent nor overlapping.

  attribute `sqlalchemy.dialects.postgresql.Range.`upper: _T | None

    the upper bound

  attribute `sqlalchemy.dialects.postgresql.Range.`upper_inc

    Return True if the upper bound is inclusive.

  attribute `sqlalchemy.dialects.postgresql.Range.`upper_inf

    Return True if this range is non-empty and the upper bound is infinite.

### Multiranges

Multiranges are supported by PostgreSQL 14 and above. SQLAlchemy’s multirange datatypes deal in lists of `Range` types.

Multiranges are supported on the psycopg, asyncpg, and pg8000 dialects only. The psycopg2 dialect, which is SQLAlchemy’s default `postgresql` dialect, does not support multirange datatypes.

Added in version 2.0: Added support for MULTIRANGE datatypes. SQLAlchemy represents a multirange value as a list of `Range` objects.

Added in version 2.0.17: Added multirange support for the pg8000 dialect. pg8000 1.29.8 or greater is required.

Added in version 2.0.26: `MultiRange` sequence added.

The example below illustrates use of the `TSMULTIRANGE` datatype:

    from datetime import datetime
    from typing import List

    from sqlalchemy.dialects.postgresql import Range
    from sqlalchemy.dialects.postgresql import TSMULTIRANGE
    from sqlalchemy.orm import DeclarativeBase
    from sqlalchemy.orm import Mapped
    from sqlalchemy.orm import mapped_column

    class Base(DeclarativeBase):
        pass

    class EventCalendar(Base):
        __tablename__ = "event_calendar"

        id: Mapped[int] = mapped_column(primary_key=True)
        event_name: Mapped[str]
        added: Mapped[datetime]
        in_session_periods: Mapped[List[Range[datetime]]] = mapped_column(TSMULTIRANGE)

Illustrating insertion and selecting of a record:

    from sqlalchemy import create_engine
    from sqlalchemy import select
    from sqlalchemy.orm import Session

    engine = create_engine("postgresql+psycopg://scott:tiger@pg14/test")

    Base.metadata.create_all(engine)

    with Session(engine) as session:
        calendar = EventCalendar(
            event_name="SQLAlchemy Tutorial Sessions",
            in_session_periods=[
                Range(datetime(2013, 3, 23), datetime(2013, 3, 25)),
                Range(datetime(2013, 4, 12), datetime(2013, 4, 15)),
                Range(datetime(2013, 5, 9), datetime(2013, 5, 12)),
            ],
        )
        session.add(calendar)
        session.commit()

        for multirange in session.scalars(select(EventCalendar.in_session_periods)):
            for range_ in multirange:
                print(f"Start: {range_.lower}  End: {range_.upper}")

Note

In the above example, the list of `Range` types as handled by the ORM will not automatically detect in-place changes to a particular list value; to update list values with the ORM, either re-assign a new list to the attribute, or use the `MutableList` type modifier. See the section Mutation Tracking for background.

#### Use of a MultiRange sequence to infer the multirange type

When using a multirange as a literal without specifying the type the utility `MultiRange` sequence can be used:

    from sqlalchemy import literal
    from sqlalchemy.dialects.postgresql import MultiRange

    with Session(engine) as session:
        stmt = select(EventCalendar).where(
            EventCalendar.added.op("<@")(
                MultiRange(
                    [
                        Range(datetime(2023, 1, 1), datetime(2013, 3, 31)),
                        Range(datetime(2023, 7, 1), datetime(2013, 9, 30)),
                    ]
                )
            )
        )
        in_range = session.execute(stmt).all()

    with engine.connect() as conn:
        row = conn.scalar(select(literal(MultiRange([Range(2, 4)]))))
        print(f"{row.lower} -> {row.upper}")

Using a simple `list` instead of `MultiRange` would require manually setting the type of the literal value to the appropriate multirange type.

Added in version 2.0.26: `MultiRange` sequence added.

The available multirange datatypes are as follows:

- `INT4MULTIRANGE`

- `INT8MULTIRANGE`

- `NUMMULTIRANGE`

- `DATEMULTIRANGE`

- `TSMULTIRANGE`

- `TSTZMULTIRANGE`

## Network Data Types

The included networking datatypes are `INET`, `CIDR`, `MACADDR`.

For `INET` and `CIDR` datatypes, conditional support is available for these datatypes to send and retrieve Python `ipaddress` objects including `ipaddress.IPv4Network`, `ipaddress.IPv6Network`, `ipaddress.IPv4Address`, `ipaddress.IPv6Address`. This support is currently the default behavior of the DBAPI itself, and varies per DBAPI. SQLAlchemy does not yet implement its own network address conversion logic.

- The psycopg and asyncpg support these datatypes fully; objects from the `ipaddress` family are returned in rows by default.

- The psycopg2 dialect only sends and receives strings.

- The pg8000 dialect supports `ipaddress.IPv4Address` and `ipaddress.IPv6Address` objects for the `INET` datatype, but uses strings for `CIDR` types.

To normalize all the above DBAPIs to only return strings, use the `native_inet_types` parameter, passing a value of `False`:

    e = create_engine(
        "postgresql+psycopg://scott:tiger@host/dbname", native_inet_types=False
    )

With the above parameter, the `psycopg`, `asyncpg` and `pg8000` dialects will disable the DBAPI’s adaptation of these types and will return only strings, matching the behavior of the older `psycopg2` dialect.

The parameter may also be set to `True`, where it will have the effect of raising `NotImplementedError` for those backends that don’t support, or don’t yet fully support, conversion of rows to Python `ipaddress` datatypes (currently psycopg2 and pg8000).

Added in version 2.0.18: - added the `native_inet_types` parameter.

## PostgreSQL Data Types

As with all SQLAlchemy dialects, all UPPERCASE types that are known to be valid with PostgreSQL are importable from the top level dialect, whether they originate from `sqlalchemy.types` or from the local dialect:

    from sqlalchemy.dialects.postgresql import (
        ARRAY,
        BIGINT,
        BIT,
        BOOLEAN,
        BYTEA,
        CHAR,
        CIDR,
        CITEXT,
        DATE,
        DATEMULTIRANGE,
        DATERANGE,
        DOMAIN,
        DOUBLE_PRECISION,
        ENUM,
        FLOAT,
        HSTORE,
        INET,
        INT4MULTIRANGE,
        INT4RANGE,
        INT8MULTIRANGE,
        INT8RANGE,
        INTEGER,
        INTERVAL,
        JSON,
        JSONB,
        JSONPATH,
        MACADDR,
        MACADDR8,
        MONEY,
        NUMERIC,
        NUMMULTIRANGE,
        NUMRANGE,
        OID,
        REAL,
        REGCLASS,
        REGCONFIG,
        SMALLINT,
        TEXT,
        TIME,
        TIMESTAMP,
        TSMULTIRANGE,
        TSQUERY,
        TSRANGE,
        TSTZMULTIRANGE,
        TSTZRANGE,
        TSVECTOR,
        UUID,
        VARCHAR,
    )

Types which are specific to PostgreSQL, or have PostgreSQL-specific construction arguments, are as follows:

Object Name | Description
--- | ---
AbstractMultiRange | Base for PostgreSQL MULTIRANGE types.
AbstractRange | Base class for single and multi Range SQL types.
AbstractSingleRange | Base for PostgreSQL RANGE types.
ARRAY | PostgreSQL ARRAY type.
BIT |
BYTEA |
CIDR |
CITEXT | Provide the PostgreSQL CITEXT type.
DATEMULTIRANGE | Represent the PostgreSQL DATEMULTIRANGE type.
DATERANGE | Represent the PostgreSQL DATERANGE type.
DOMAIN | Represent the DOMAIN PostgreSQL type.
ENUM | PostgreSQL ENUM type.
HSTORE | Represent the PostgreSQL HSTORE type.
INET |
INT4MULTIRANGE | Represent the PostgreSQL INT4MULTIRANGE type.
INT4RANGE | Represent the PostgreSQL INT4RANGE type.
INT8MULTIRANGE | Represent the PostgreSQL INT8MULTIRANGE type.
INT8RANGE | Represent the PostgreSQL INT8RANGE type.
INTERVAL | PostgreSQL INTERVAL type.
JSON | Represent the PostgreSQL JSON type.
JSONB | Represent the PostgreSQL JSONB type.
JSONPATH | JSON Path Type.
MACADDR |
MACADDR8 |
MONEY | Provide the PostgreSQL MONEY type.
MultiRange | Represents a multirange sequence.
NUMMULTIRANGE | Represent the PostgreSQL NUMMULTIRANGE type.
NUMRANGE | Represent the PostgreSQL NUMRANGE type.
OID | Provide the PostgreSQL OID type.
REGCLASS | Provide the PostgreSQL REGCLASS type.
REGCONFIG | Provide the PostgreSQL REGCONFIG type.
TIME | PostgreSQL TIME type.
TIMESTAMP | Provide the PostgreSQL TIMESTAMP type.
TSMULTIRANGE | Represent the PostgreSQL TSRANGE type.
TSQUERY | Provide the PostgreSQL TSQUERY type.
TSRANGE | Represent the PostgreSQL TSRANGE type.
TSTZMULTIRANGE | Represent the PostgreSQL TSTZRANGE type.
TSTZRANGE | Represent the PostgreSQL TSTZRANGE type.
TSVECTOR | The `TSVECTOR` type implements the PostgreSQL text search type TSVECTOR.

class sqlalchemy.dialects.postgresql.AbstractRange

  inherits from `sqlalchemy.types.TypeEngine`

  Base class for single and multi Range SQL types.

  Member Name | Description
  --- | ---
  adjacent_to() | Boolean expression. Returns true if the range in the column is adjacent to the range in the operand.
  contained_by() | Boolean expression. Returns true if the column is contained within the right hand operand.
  contains() | Boolean expression. Returns true if the right hand operand, which can be an element or a range, is contained within the column.
  difference() | Range expression. Returns the union of the two ranges. Will raise an exception if the resulting range is not contiguous.
  intersection() | Range expression. Returns the intersection of the two ranges. Will raise an exception if the resulting range is not contiguous.
  not_extend_left_of() | Boolean expression. Returns true if the range in the column does not extend left of the range in the operand.
  not_extend_right_of() | Boolean expression. Returns true if the range in the column does not extend right of the range in the operand.
  overlaps() | Boolean expression. Returns true if the column overlaps (has points in common with) the right hand operand.
  strictly_left_of() | Boolean expression. Returns true if the column is strictly left of the right hand operand.
  strictly_right_of() | Boolean expression. Returns true if the column is strictly right of the right hand operand.
  union() | Range expression. Returns the union of the two ranges. Will raise an exception if the resulting range is not contiguous.

  class comparator_factory

    inherits from `sqlalchemy.types.Comparator`

    Define comparison operations for range types.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`adjacent_to(other: Any) → ColumnElement[bool]

      Boolean expression. Returns true if the range in the column is adjacent to the range in the operand.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`contained_by(other: Any) → ColumnElement[bool]

      Boolean expression. Returns true if the column is contained within the right hand operand.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`contains(other: Any, **kw: Any) → ColumnElement[bool]

      Boolean expression. Returns true if the right hand operand, which can be an element or a range, is contained within the column.

      kwargs may be ignored by this operator but are required for API conformance.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`difference(other: Any) → ColumnElement[bool]

      Range expression. Returns the union of the two ranges. Will raise an exception if the resulting range is not contiguous.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`intersection(other: Any) → ColumnElement[Range[_T]]

      Range expression. Returns the intersection of the two ranges. Will raise an exception if the resulting range is not contiguous.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`not_extend_left_of(other: Any) → ColumnElement[bool]

      Boolean expression. Returns true if the range in the column does not extend left of the range in the operand.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`not_extend_right_of(other: Any) → ColumnElement[bool]

      Boolean expression. Returns true if the range in the column does not extend right of the range in the operand.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`overlaps(other: Any) → ColumnElement[bool]

      Boolean expression. Returns true if the column overlaps (has points in common with) the right hand operand.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`strictly_left_of(other: Any) → ColumnElement[bool]

      Boolean expression. Returns true if the column is strictly left of the right hand operand.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`strictly_right_of(other: Any) → ColumnElement[bool]

      Boolean expression. Returns true if the column is strictly right of the right hand operand.

    method `sqlalchemy.dialects.postgresql.AbstractRange.comparator_factory.`union(other: Any) → ColumnElement[bool]

      Range expression. Returns the union of the two ranges. Will raise an exception if the resulting range is not contiguous.

class sqlalchemy.dialects.postgresql.AbstractSingleRange

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractRange`

  Base for PostgreSQL RANGE types.

  These are types that return a single `Range` object.

  See also

  PostgreSQL range functions

class sqlalchemy.dialects.postgresql.AbstractMultiRange

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractRange`

  Base for PostgreSQL MULTIRANGE types.

  these are types that return a sequence of `Range` objects.

class sqlalchemy.dialects.postgresql.ARRAY

  inherits from `sqlalchemy.types.ARRAY`

  PostgreSQL ARRAY type.

  The `ARRAY` type is constructed in the same way as the core `ARRAY` type; a member type is required, and a number of dimensions is recommended if the type is to be used for more than one dimension:

      from sqlalchemy.dialects import postgresql

      mytable = Table(
          "mytable",
          metadata,
          Column("data", postgresql.ARRAY(Integer, dimensions=2)),
      )

  The `ARRAY` type provides all operations defined on the core `ARRAY` type, including support for “dimensions”, indexed access, and simple matching such as `Comparator.any()` and `Comparator.all()`. `ARRAY` class also provides PostgreSQL-specific methods for containment operations, including `Comparator.contains()` `Comparator.contained_by()`, and `Comparator.overlap()`, e.g.:

      mytable.c.data.contains([1, 2])

  Indexed access is one-based by default, to match that of PostgreSQL; for zero-based indexed access, set `ARRAY.zero_indexes`.

  Additionally, the `ARRAY` type does not work directly in conjunction with the `ENUM` type. For a workaround, see the special type at Using ENUM with ARRAY.

  Detecting Changes in ARRAY columns when using the ORM

  The `ARRAY` type, when used with the SQLAlchemy ORM, does not detect in-place mutations to the array. In order to detect these, the `sqlalchemy.ext.mutable` extension must be used, using the `MutableList` class:

      from sqlalchemy.dialects.postgresql import ARRAY
      from sqlalchemy.ext.mutable import MutableList

      class SomeOrmClass(Base):
          # ...

          data = Column(MutableList.as_mutable(ARRAY(Integer)))

  This extension will allow “in-place” changes such to the array such as `.append()` to produce events which will be detected by the unit of work. Note that changes to elements inside the array, including subarrays that are mutated in place, are not detected.

  Alternatively, assigning a new array value to an ORM element that replaces the old one will always trigger a change event.

  See also

  `ARRAY` - base array type

  `array` - produces a literal array value.

  Member Name | Description
  --- | ---
  __init__() | Construct an ARRAY.
  contains() | Boolean expression. Test if elements are a superset of the elements of the argument array expression.
  contained_by() | Boolean expression. Test if elements are a proper subset of the elements of the argument array expression.
  overlap() | Boolean expression. Test if array has elements in common with an argument array expression.

  method `sqlalchemy.dialects.postgresql.ARRAY.`__init__(item_type: _TypeEngineArgument[_T], as_tuple: bool = False, dimensions: int | None = None, zero_indexes: bool = False)

    Construct an ARRAY.

    E.g.:

        Column("myarray", ARRAY(Integer))

    Arguments are:

    Parameters:

      - item_type – The data type of items of this array. Note that dimensionality is irrelevant here, so multi-dimensional arrays like `INTEGER[][]`, are constructed as `ARRAY(Integer)`, not as `ARRAY(ARRAY(Integer))` or such.

      - as_tuple=False – Specify whether return results should be converted to tuples from lists. DBAPIs such as psycopg2 return lists by default. When tuples are returned, the results are hashable.

      - dimensions – if non-None, the ARRAY will assume a fixed number of dimensions. This will cause the DDL emitted for this ARRAY to include the exact number of bracket clauses `[]`, and will also optimize the performance of the type overall. Note that PG arrays are always implicitly “non-dimensioned”, meaning they can store any number of dimensions no matter how they were declared.

      - zero_indexes=False – when True, index values will be converted between Python zero-based and PostgreSQL one-based indexes, e.g. a value of one will be added to all index values before passing to the database.

  class Comparator

    inherits from `sqlalchemy.types.Comparator`

    Define comparison operations for `ARRAY`.

    Note that these operations are in addition to those provided by the base `Comparator` class, including `Comparator.any()` and `Comparator.all()`.

    method `sqlalchemy.dialects.postgresql.ARRAY.Comparator.`contains(other: typing_Any, **kwargs: typing_Any) → ColumnElement[bool]

      Boolean expression. Test if elements are a superset of the elements of the argument array expression.

      kwargs may be ignored by this operator but are required for API conformance.

    method `sqlalchemy.dialects.postgresql.ARRAY.Comparator.`contained_by(other: typing_Any) → ColumnElement[bool]

      Boolean expression. Test if elements are a proper subset of the elements of the argument array expression.

    method `sqlalchemy.dialects.postgresql.ARRAY.Comparator.`overlap(other: typing_Any) → ColumnElement[bool]

      Boolean expression. Test if array has elements in common with an argument array expression.

class sqlalchemy.dialects.postgresql.BIT

  inherits from `sqlalchemy.types.TypeEngine`

class sqlalchemy.dialects.postgresql.BYTEA

  inherits from `sqlalchemy.types.LargeBinary`

  Member Name | Description
  --- | ---
  __init__() | Construct a LargeBinary type.

  method `sqlalchemy.dialects.postgresql.BYTEA.`__init__(length: int | None = None)

    inherited from the `sqlalchemy.types.LargeBinary.__init__` method of `LargeBinary`

    Construct a LargeBinary type.

    Parameters:

      length – optional, a length for the column for use in DDL statements, for those binary types that accept a length, such as the MySQL BLOB type.

class sqlalchemy.dialects.postgresql.CIDR

  inherits from `sqlalchemy.dialects.postgresql.types._NetworkAddressTypeMixin`, `sqlalchemy.types.TypeEngine`

class sqlalchemy.dialects.postgresql.CITEXT

  inherits from `sqlalchemy.types.TEXT`

  Provide the PostgreSQL CITEXT type.

  Added in version 2.0.7.

  Member Name | Description
  --- | ---
  __init__() | Create a string-holding type.

  method `sqlalchemy.dialects.postgresql.CITEXT.`__init__(length: int | None = None, collation: str | None = None)

    inherited from the `sqlalchemy.types.String.__init__` method of `String`

    Create a string-holding type.

    Parameters:

      - length – optional, a length for the column for use in DDL and CAST expressions. May be safely omitted if no `CREATE TABLE` will be issued. Certain databases may require a `length` for use in DDL, and will raise an exception when the `CREATE TABLE` DDL is issued if a `VARCHAR` with no length is included. Whether the value is interpreted as bytes or characters is database specific.

      - collation –

        Optional, a column-level collation for use in DDL and CAST expressions. Renders using the COLLATE keyword supported by SQLite, MySQL, and PostgreSQL. E.g.:

            >>> from sqlalchemy import cast, select, String
            >>> print(select(cast("some string", String(collation="utf8"))))
            SELECT CAST(:param_1 AS VARCHAR COLLATE utf8) AS anon_1

        Note

        In most cases, the `Unicode` or `UnicodeText` datatypes should be used for a `Column` that expects to store non-ascii data. These datatypes will ensure that the correct types are used on the database.

class sqlalchemy.dialects.postgresql.DOMAIN

  inherits from `sqlalchemy.dialects.postgresql.named_types.NamedType`, `sqlalchemy.types.SchemaType`

  Represent the DOMAIN PostgreSQL type.

  A domain is essentially a data type with optional constraints that restrict the allowed set of values. E.g.:

      PositiveInt = DOMAIN("pos_int", Integer, check="VALUE > 0", not_null=True)

      UsPostalCode = DOMAIN(
          "us_postal_code",
          Text,
          check="VALUE ~ '^\d{5}$' OR VALUE ~ '^\d{5}-\d{4}$'",
      )

  See the PostgreSQL documentation for additional details

  Added in version 2.0.

  Member Name | Description
  --- | ---
  __init__() | Construct a DOMAIN.
  create() | Emit `CREATE` DDL for this type.
  drop() | Emit `DROP` DDL for this type.

  method `sqlalchemy.dialects.postgresql.DOMAIN.`__init__(name: str, data_type: _TypeEngineArgument[Any], *, collation: str | None = None, default: elements.TextClause | str | None = None, constraint_name: str | None = None, not_null: bool | None = None, check: elements.TextClause | str | None = None, create_type: bool = True, **kw: Any)

    Construct a DOMAIN.

    Parameters:

      - name – the name of the domain

      - data_type – The underlying data type of the domain. This can include array specifiers.

      - collation – An optional collation for the domain. If no collation is specified, the underlying data type’s default collation is used. The underlying type must be collatable if `collation` is specified.

      - default – The DEFAULT clause specifies a default value for columns of the domain data type. The default should be a string or a `text()` value. If no default value is specified, then the default value is the null value.

      - constraint_name – An optional name for a constraint. If not specified, the backend generates a name.

      - not_null – Values of this domain are prevented from being null. By default domain are allowed to be null. If not specified no nullability clause will be emitted.

      - check – CHECK clause specify integrity constraint or test which values of the domain must satisfy. A constraint must be an expression producing a Boolean result that can use the key word VALUE to refer to the value being tested. Differently from PostgreSQL, only a single check clause is currently allowed in SQLAlchemy.

      - schema – optional schema name

      - metadata – optional `MetaData` object which this `DOMAIN` will be directly associated

      - create_type – Defaults to True. Indicates that `CREATE TYPE` should be emitted, after optionally checking for the presence of the type, when the parent table is being created; and additionally that `DROP TYPE` is called when the table is dropped.

  method `sqlalchemy.dialects.postgresql.DOMAIN.`create(bind: _CreateDropBind, checkfirst: bool = True, **kw: Any) → None

    inherited from the `NamedType.create()` method of `NamedType`

    Emit `CREATE` DDL for this type.

    Parameters:

      - bind – a connectable `Engine`, `Connection`, or similar object to emit SQL.

      - checkfirst – if `True`, a query against the PG catalog will be first performed to see if the type does not exist already before creating.

  method `sqlalchemy.dialects.postgresql.DOMAIN.`drop(bind: _CreateDropBind, checkfirst: bool = True, **kw: Any) → None

    inherited from the `NamedType.drop()` method of `NamedType`

    Emit `DROP` DDL for this type.

    Parameters:

      - bind – a connectable `Engine`, `Connection`, or similar object to emit SQL.

      - checkfirst – if `True`, a query against the PG catalog will be first performed to see if the type actually exists before dropping.

class sqlalchemy.dialects.postgresql.DOUBLE_PRECISION

  inherits from `sqlalchemy.types.Double`

  The SQL DOUBLE PRECISION type.

  Added in version 2.0.

  See also

  `Double` - documentation for the base type.

  method `sqlalchemy.dialects.postgresql.DOUBLE_PRECISION.`__init__(precision: int | None = None, asdecimal: bool = False, decimal_return_scale: int | None = None)

    inherited from the `sqlalchemy.types.Float.__init__` method of `Float`

    Construct a Float.

    Parameters:

      - precision –

        the numeric precision for use in DDL `CREATE TABLE`. Backends should attempt to ensure this precision indicates a number of digits for the generic `Float` datatype.

        Note

        For the Oracle Database backend, the `Float.precision` parameter is not accepted when rendering DDL, as Oracle Database does not support float precision specified as a number of decimal places. Instead, use the Oracle Database-specific `FLOAT` datatype and specify the `FLOAT.binary_precision` parameter. This is new in version 2.0 of SQLAlchemy.

        To create a database agnostic `Float` that separately specifies binary precision for Oracle Database, use `TypeEngine.with_variant()` as follows:

            from sqlalchemy import Column
            from sqlalchemy import Float
            from sqlalchemy.dialects import oracle

            Column(
                "float_data",
                Float(5).with_variant(oracle.FLOAT(binary_precision=16), "oracle"),
            )

      - asdecimal – the same flag as that of `Numeric`, but defaults to `False`. Note that setting this flag to `True` results in floating point conversion.

      - decimal_return_scale – Default scale to use when converting from floats to Python decimals. Floating point values will typically be much longer due to decimal inaccuracy, and most floating point database types don’t have a notion of “scale”, so by default the float type looks for the first ten decimal places when converting. Specifying this value will override that length. Note that the MySQL float types, which do include “scale”, will use “scale” as the default for decimal_return_scale, if not otherwise specified.

class sqlalchemy.dialects.postgresql.ENUM

  inherits from `sqlalchemy.dialects.postgresql.named_types.NamedType`, `sqlalchemy.types.NativeForEmulated`, `sqlalchemy.types.Enum`

  PostgreSQL ENUM type.

  This is a subclass of `Enum` which includes support for PG’s `CREATE TYPE` and `DROP TYPE`.

  When the builtin type `Enum` is used and the `Enum.native_enum` flag is left at its default of True, the PostgreSQL backend will use a `ENUM` type as the implementation, so the special create/drop rules will be used.

  The create/drop behavior of ENUM is necessarily intricate, due to the awkward relationship the ENUM type has in relationship to the parent table, in that it may be “owned” by just a single table, or may be shared among many tables.

  When using `Enum` or `ENUM` in an “inline” fashion, the `CREATE TYPE` and `DROP TYPE` is emitted corresponding to when the `Table.create()` and `Table.drop()` methods are called:

      table = Table(
          "sometable",
          metadata,
          Column("some_enum", ENUM("a", "b", "c", name="myenum")),
      )

      table.create(engine)  # will emit CREATE ENUM and CREATE TABLE
      table.drop(engine)  # will emit DROP TABLE and DROP ENUM

  To use a common enumerated type between multiple tables, the best practice is to declare the `Enum` or `ENUM` independently, and associate it with the `MetaData` object itself:

      my_enum = ENUM("a", "b", "c", name="myenum", metadata=metadata)

      t1 = Table("sometable_one", metadata, Column("some_enum", myenum))

      t2 = Table("sometable_two", metadata, Column("some_enum", myenum))

  When this pattern is used, care must still be taken at the level of individual table creates. Emitting CREATE TABLE without also specifying `checkfirst=True` will still cause issues:

      t1.create(engine)  # will fail: no such type 'myenum'

  If we specify `checkfirst=True`, the individual table-level create operation will check for the `ENUM` and create if not exists:

      # will check if enum exists, and emit CREATE TYPE if not
      t1.create(engine, checkfirst=True)

  When using a metadata-level ENUM type, the type will always be created and dropped if either the metadata-wide create/drop is called:

      metadata.create_all(engine)  # will emit CREATE TYPE
      metadata.drop_all(engine)  # will emit DROP TYPE

  The type can also be created and dropped directly:

      my_enum.create(engine)
      my_enum.drop(engine)

  Member Name | Description
  --- | ---
  __init__() | Construct an `ENUM`.
  create() | Emit `CREATE TYPE` for this `ENUM`.
  drop() | Emit `DROP TYPE` for this `ENUM`.

  method `sqlalchemy.dialects.postgresql.ENUM.`__init__(*enums, name: str | _NoArg | None = _NoArg.NO_ARG, create_type: bool = True, **kw)

    Construct an `ENUM`.

    Arguments are the same as that of `Enum`, but also including the following parameters.

    Parameters:

      create_type – Defaults to True. Indicates that `CREATE TYPE` should be emitted, after optionally checking for the presence of the type, when the parent table is being created; and additionally that `DROP TYPE` is called when the table is dropped. When `False`, no check will be performed and no `CREATE TYPE` or `DROP TYPE` is emitted, unless `ENUM.create()` or `ENUM.drop()` are called directly. Setting to `False` is helpful when invoking a creation scheme to a SQL file without access to the actual database - the `ENUM.create()` and `ENUM.drop()` methods can be used to emit SQL to a target bind.

  method `sqlalchemy.dialects.postgresql.ENUM.`create(bind: _CreateDropBind, checkfirst: bool = True) → None

    Emit `CREATE TYPE` for this `ENUM`.

    If the underlying dialect does not support PostgreSQL CREATE TYPE, no action is taken.

    Parameters:

      - bind – a connectable `Engine`, `Connection`, or similar object to emit SQL.

      - checkfirst – if `True`, a query against the PG catalog will be first performed to see if the type does not exist already before creating.

  method `sqlalchemy.dialects.postgresql.ENUM.`drop(bind: _CreateDropBind, checkfirst: bool = True) → None

    Emit `DROP TYPE` for this `ENUM`.

    If the underlying dialect does not support PostgreSQL DROP TYPE, no action is taken.

    Parameters:

      - bind – a connectable `Engine`, `Connection`, or similar object to emit SQL.

      - checkfirst – if `True`, a query against the PG catalog will be first performed to see if the type actually exists before dropping.

class sqlalchemy.dialects.postgresql.HSTORE

  inherits from `sqlalchemy.types.Indexable`, `sqlalchemy.types.Concatenable`, `sqlalchemy.types.TypeEngine`

  Represent the PostgreSQL HSTORE type.

  The `HSTORE` type stores dictionaries containing strings, e.g.:

      data_table = Table(
          "data_table",
          metadata,
          Column("id", Integer, primary_key=True),
          Column("data", HSTORE),
      )

      with engine.connect() as conn:
          conn.execute(
              data_table.insert(), data={"key1": "value1", "key2": "value2"}
          )

  `HSTORE` provides for a wide range of operations, including:

  - Index operations:

        data_table.c.data["some key"] == "some value"

  - Containment operations:

        data_table.c.data.has_key("some key")

        data_table.c.data.has_all(["one", "two", "three"])

  - Concatenation:

        data_table.c.data + {"k1": "v1"}

  For a full list of special methods see `comparator_factory`.

  Detecting Changes in HSTORE columns when using the ORM

  For usage with the SQLAlchemy ORM, it may be desirable to combine the usage of `HSTORE` with `MutableDict` dictionary now part of the `sqlalchemy.ext.mutable` extension. This extension will allow “in-place” changes to the dictionary, e.g. addition of new keys or replacement/removal of existing keys to/from the current dictionary, to produce events which will be detected by the unit of work:

      from sqlalchemy.ext.mutable import MutableDict

      class MyClass(Base):
          __tablename__ = "data_table"

          id = Column(Integer, primary_key=True)
          data = Column(MutableDict.as_mutable(HSTORE))

      my_object = session.query(MyClass).one()

      # in-place mutation, requires Mutable extension
      # in order for the ORM to detect
      my_object.data["some_key"] = "some value"

      session.commit()

  When the `sqlalchemy.ext.mutable` extension is not used, the ORM will not be alerted to any changes to the contents of an existing dictionary, unless that dictionary value is re-assigned to the HSTORE-attribute itself, thus generating a change event.

  See also

  `hstore` - render the PostgreSQL `hstore()` function.

  Member Name | Description
  --- | ---
  array() | Text array expression. Returns array of alternating keys and values.
  contained_by() | Boolean expression. Test if keys are a proper subset of the keys of the argument jsonb expression.
  contains() | Boolean expression. Test if keys (or array) are a superset of/contained the keys of the argument jsonb expression.
  defined() | Boolean expression. Test for presence of a non-NULL value for the key. Note that the key may be a SQLA expression.
  delete() | HStore expression. Returns the contents of this hstore with the given key deleted. Note that the key may be a SQLA expression.
  has_all() | Boolean expression. Test for presence of all keys in jsonb
  has_any() | Boolean expression. Test for presence of any key in jsonb
  has_key() | Boolean expression. Test for presence of a key. Note that the key may be a SQLA expression.
  keys() | Text array expression. Returns array of keys.
  matrix() | Text array expression. Returns array of [key, value] pairs.
  slice() | HStore expression. Returns a subset of an hstore defined by array of keys.
  vals() | Text array expression. Returns array of values.
  __init__() | Construct a new `HSTORE`.
  bind_processor() | Return a conversion function for processing bind values.
  comparator_factory | alias of `Comparator`
  hashable | Flag, if False, means values from this type aren’t hashable.
  result_processor() | Return a conversion function for processing result row values.

  class Comparator

    inherits from `sqlalchemy.types.Comparator`, `sqlalchemy.types.Comparator`

    Define comparison operations for `HSTORE`.

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`array()

      Text array expression. Returns array of alternating keys and values.

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`contained_by(other)

      Boolean expression. Test if keys are a proper subset of the keys of the argument jsonb expression.

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`contains(other, **kwargs)

      Boolean expression. Test if keys (or array) are a superset of/contained the keys of the argument jsonb expression.

      kwargs may be ignored by this operator but are required for API conformance.

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`defined(key)

      Boolean expression. Test for presence of a non-NULL value for the key. Note that the key may be a SQLA expression.

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`delete(key)

      HStore expression. Returns the contents of this hstore with the given key deleted. Note that the key may be a SQLA expression.

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`has_all(other)

      Boolean expression. Test for presence of all keys in jsonb

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`has_any(other)

      Boolean expression. Test for presence of any key in jsonb

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`has_key(other)

      Boolean expression. Test for presence of a key. Note that the key may be a SQLA expression.

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`keys()

      Text array expression. Returns array of keys.

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`matrix()

      Text array expression. Returns array of [key, value] pairs.

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`slice(array)

      HStore expression. Returns a subset of an hstore defined by array of keys.

    method `sqlalchemy.dialects.postgresql.HSTORE.Comparator.`vals()

      Text array expression. Returns array of values.

  method `sqlalchemy.dialects.postgresql.HSTORE.`__init__(text_type=None)

    Construct a new `HSTORE`.

    Parameters:

      text_type – the type that should be used for indexed values. Defaults to `Text`.

  method `sqlalchemy.dialects.postgresql.HSTORE.`bind_processor(dialect)

    Return a conversion function for processing bind values.

    Returns a callable which will receive a bind parameter value as the sole positional argument and will return a value to send to the DB-API.

    If processing is not necessary, the method should return `None`.

    Tip

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.bind_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.bind_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_bind_param()`.

    See also

    Augmenting Existing Types

    Parameters:

      dialect – Dialect instance in use.

  attribute `sqlalchemy.dialects.postgresql.HSTORE.`comparator_factory

    alias of `Comparator`

  attribute `sqlalchemy.dialects.postgresql.HSTORE.`hashable = False

    Flag, if False, means values from this type aren’t hashable.

    Used by the ORM when uniquing result lists.

  method `sqlalchemy.dialects.postgresql.HSTORE.`result_processor(dialect, coltype)

    Return a conversion function for processing result row values.

    Returns a callable which will receive a result row column value as the sole positional argument and will return a value to return to the user.

    If processing is not necessary, the method should return `None`.

    Tip

    This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it’s not feasible to subclass a `TypeEngine` class in order to provide an alternate `TypeEngine.result_processor()` method, unless subclassing the `UserDefinedType` class explicitly.

    To provide alternate behavior for `TypeEngine.result_processor()`, implement a `TypeDecorator` class and provide an implementation of `TypeDecorator.process_result_value()`.

    See also

    Augmenting Existing Types

    Parameters:

      - dialect – Dialect instance in use.

      - coltype – DBAPI coltype argument received in cursor.description.

class sqlalchemy.dialects.postgresql.INET

  inherits from `sqlalchemy.dialects.postgresql.types._NetworkAddressTypeMixin`, `sqlalchemy.types.TypeEngine`

class sqlalchemy.dialects.postgresql.INTERVAL

  inherits from `sqlalchemy.types.NativeForEmulated`, `sqlalchemy.types._AbstractInterval`

  PostgreSQL INTERVAL type.

  Member Name | Description
  --- | ---
  __init__() | Construct an INTERVAL.

  method `sqlalchemy.dialects.postgresql.INTERVAL.`__init__(precision: int | None = None, fields: str | None = None) → None

    Construct an INTERVAL.

    Parameters:

      - precision – optional integer precision value

      - fields –

        string fields specifier. allows storage of fields to be limited, such as `"YEAR"`, `"MONTH"`, `"DAY TO HOUR"`, etc.

        Added in version 1.2.

class sqlalchemy.dialects.postgresql.JSON

  inherits from `sqlalchemy.types.JSON`

  Represent the PostgreSQL JSON type.

  `JSON` is used automatically whenever the base `JSON` datatype is used against a PostgreSQL backend, however base `JSON` datatype does not provide Python accessors for PostgreSQL-specific comparison methods such as `Comparator.astext()`; additionally, to use PostgreSQL `JSONB`, the `JSONB` datatype should be used explicitly.

  See also

  `JSON` - main documentation for the generic cross-platform JSON datatype.

  The operators provided by the PostgreSQL version of `JSON` include:

  - Index operations (the `->` operator):

        data_table.c.data["some key"]

        data_table.c.data[5]

  - Index operations returning text (the `->>` operator):

        data_table.c.data["some key"].astext == "some value"

    Note that equivalent functionality is available via the `Comparator.as_string` accessor.

  - Index operations with CAST (equivalent to `CAST(col ->> ['some key'] AS <type>)`):

        data_table.c.data["some key"].astext.cast(Integer) == 5

    Note that equivalent functionality is available via the `Comparator.as_integer` and similar accessors.

  - Path index operations (the `#>` operator):

        data_table.c.data[("key_1", "key_2", 5, ..., "key_n")]

  - Path index operations returning text (the `#>>` operator):

        data_table.c.data[
            ("key_1", "key_2", 5, ..., "key_n")
        ].astext == "some value"

  Index operations return an expression object whose type defaults to `JSON` by default, so that further JSON-oriented instructions may be called upon the result type.

  Custom serializers and deserializers are specified at the dialect level, that is using `create_engine()`. The reason for this is that when using psycopg2, the DBAPI only allows serializers at the per-cursor or per-connection level. E.g.:

      engine = create_engine(
          "postgresql+psycopg2://scott:tiger@localhost/test",
          json_serializer=my_serialize_fn,
          json_deserializer=my_deserialize_fn,
      )

  When using the psycopg2 dialect, the json_deserializer is registered against the database using `psycopg2.extras.register_default_json`.

  See also

  `JSON` - Core level JSON type

  `JSONB`

  Member Name | Description
  --- | ---
  astext | On an indexed expression, use the “astext” (e.g. “->>”) conversion when rendered in SQL.
  __init__() | Construct a `JSON` type.
  comparator_factory | alias of `Comparator`
  render_bind_cast | Render bind casts for `BindTyping.RENDER_CASTS` mode.

  class Comparator

    inherits from `sqlalchemy.types.Comparator`

    Define comparison operations for `JSON`.

    attribute `sqlalchemy.dialects.postgresql.JSON.Comparator.`astext

      On an indexed expression, use the “astext” (e.g. “->>”) conversion when rendered in SQL.

      E.g.:

          select(data_table.c.data["some key"].astext)

      See also

      `ColumnElement.cast()`

  method `sqlalchemy.dialects.postgresql.JSON.`__init__(none_as_null: bool = False, astext_type: TypeEngine[str] | None = None)

    Construct a `JSON` type.

    Parameters:

      - none_as_null –

        if True, persist the value `None` as a SQL NULL value, not the JSON encoding of `null`. Note that when this flag is False, the `null()` construct can still be used to persist a NULL value:

            from sqlalchemy import null

            conn.execute(table.insert(), {"data": null()})

        See also

        `JSON.NULL`

      - astext_type – the type to use for the `Comparator.astext` accessor on indexed attributes. Defaults to `Text`.

  attribute `sqlalchemy.dialects.postgresql.JSON.`comparator_factory

    alias of `Comparator`

  attribute `sqlalchemy.dialects.postgresql.JSON.`render_bind_cast = True

    Render bind casts for `BindTyping.RENDER_CASTS` mode.

    If True, this type (usually a dialect level impl type) signals to the compiler that a cast should be rendered around a bound parameter for this type.

    Added in version 2.0.

    See also

    `BindTyping`

class sqlalchemy.dialects.postgresql.JSONB

  inherits from `sqlalchemy.dialects.postgresql.json.JSON`

  Represent the PostgreSQL JSONB type.

  The `JSONB` type stores arbitrary JSONB format data, e.g.:

      data_table = Table(
          "data_table",
          metadata,
          Column("id", Integer, primary_key=True),
          Column("data", JSONB),
      )

      with engine.connect() as conn:
          conn.execute(
              data_table.insert(), data={"key1": "value1", "key2": "value2"}
          )

  The `JSONB` type includes all operations provided by `JSON`, including the same behaviors for indexing operations. It also adds additional operators specific to JSONB, including `Comparator.has_key()`, `Comparator.has_all()`, `Comparator.has_any()`, `Comparator.contains()`, `Comparator.contained_by()`, `Comparator.delete_path()`, `Comparator.path_exists()` and `Comparator.path_match()`.

  Like the `JSON` type, the `JSONB` type does not detect in-place changes when used with the ORM, unless the `sqlalchemy.ext.mutable` extension is used.

  Custom serializers and deserializers are shared with the `JSON` class, using the `json_serializer` and `json_deserializer` keyword arguments. These must be specified at the dialect level using `create_engine()`. When using psycopg2, the serializers are associated with the jsonb type using `psycopg2.extras.register_default_jsonb` on a per-connection basis, in the same way that `psycopg2.extras.register_default_json` is used to register these handlers with the json type.

  See also

  `JSON`

  Warning

  For applications that have indexes against JSONB subscript expressions

  SQLAlchemy 2.0.42 made a change in how the subscript operation for `JSONB` is rendered, from `-> 'element'` to `['element']`, for PostgreSQL versions greater than 14. This change caused an unintended side effect for indexes that were created against expressions that use subscript notation, e.g. `Index("ix_entity_json_ab_text", data["a"]["b"].astext)`. If these indexes were generated with the older syntax e.g. `((entity.data -> 'a') ->> 'b')`, they will not be used by the PostgreSQL query planner when a query is made using SQLAlchemy 2.0.42 or higher on PostgreSQL versions 14 or higher. This occurs because the new text will resemble `(entity.data['a'] ->> 'b')` which will fail to produce the exact textual syntax match required by the PostgreSQL query planner. Therefore, for users upgrading to SQLAlchemy 2.0.42 or higher, existing indexes that were created against `JSONB` expressions that use subscripting would need to be dropped and re-created in order for them to work with the new query syntax, e.g. an expression like `((entity.data -> 'a') ->> 'b')` would become `(entity.data['a'] ->> 'b')`.

  See also

  #12868 - discussion of this issue

  Member Name | Description
  --- | ---
  contained_by() | Boolean expression. Test if keys are a proper subset of the keys of the argument jsonb expression (equivalent of the `<@` operator).
  contains() | Boolean expression. Test if keys (or array) are a superset of/contained the keys of the argument jsonb expression (equivalent of the `@>` operator).
  delete_path() | JSONB expression. Deletes field or array element specified in the argument array (equivalent of the `#-` operator).
  has_all() | Boolean expression. Test for presence of all keys in jsonb (equivalent of the `?&` operator)
  has_any() | Boolean expression. Test for presence of any key in jsonb (equivalent of the `?|` operator)
  has_key() | Boolean expression. Test for presence of a key (equivalent of the `?` operator). Note that the key may be a SQLA expression.
  path_exists() | Boolean expression. Test for presence of item given by the argument JSONPath expression (equivalent of the `@?` operator).
  path_match() | Boolean expression. Test if JSONPath predicate given by the argument JSONPath expression matches (equivalent of the `@@` operator).
  coerce_compared_value() | Suggest a type for a ‘coerced’ Python value in an expression.
  comparator_factory | alias of `Comparator`

  class Comparator

    inherits from `sqlalchemy.dialects.postgresql.json.Comparator`

    Define comparison operations for `JSON`.

    method `sqlalchemy.dialects.postgresql.JSONB.Comparator.`contained_by(other: Any) → ColumnElement[bool]

      Boolean expression. Test if keys are a proper subset of the keys of the argument jsonb expression (equivalent of the `<@` operator).

    method `sqlalchemy.dialects.postgresql.JSONB.Comparator.`contains(other: Any, **kwargs: Any) → ColumnElement[bool]

      Boolean expression. Test if keys (or array) are a superset of/contained the keys of the argument jsonb expression (equivalent of the `@>` operator).

      kwargs may be ignored by this operator but are required for API conformance.

    method `sqlalchemy.dialects.postgresql.JSONB.Comparator.`delete_path(array: List[str] | _pg_array[str]) → ColumnElement[JSONB]

      JSONB expression. Deletes field or array element specified in the argument array (equivalent of the `#-` operator).

      The input may be a list of strings that will be coerced to an `ARRAY` or an instance of `_postgres.array()`.

      Added in version 2.0.

    method `sqlalchemy.dialects.postgresql.JSONB.Comparator.`has_all(other: Any) → ColumnElement[bool]

      Boolean expression. Test for presence of all keys in jsonb (equivalent of the `?&` operator)

    method `sqlalchemy.dialects.postgresql.JSONB.Comparator.`has_any(other: Any) → ColumnElement[bool]

      Boolean expression. Test for presence of any key in jsonb (equivalent of the `?|` operator)

    method `sqlalchemy.dialects.postgresql.JSONB.Comparator.`has_key(other: Any) → ColumnElement[bool]

      Boolean expression. Test for presence of a key (equivalent of the `?` operator). Note that the key may be a SQLA expression.

    method `sqlalchemy.dialects.postgresql.JSONB.Comparator.`path_exists(other: Any) → ColumnElement[bool]

      Boolean expression. Test for presence of item given by the argument JSONPath expression (equivalent of the `@?` operator).

      Added in version 2.0.

    method `sqlalchemy.dialects.postgresql.JSONB.Comparator.`path_match(other: Any) → ColumnElement[bool]

      Boolean expression. Test if JSONPath predicate given by the argument JSONPath expression matches (equivalent of the `@@` operator).

      Only the first item of the result is taken into account.

      Added in version 2.0.

  method `sqlalchemy.dialects.postgresql.JSONB.`coerce_compared_value(op: OperatorType | None, value: Any) → TypeEngine[Any]

    Suggest a type for a ‘coerced’ Python value in an expression.

    Given an operator and value, gives the type a chance to return a type which the value should be coerced into.

    The default behavior here is conservative; if the right-hand side is already coerced into a SQL type based on its Python type, it is usually left alone.

    End-user functionality extension here should generally be via `TypeDecorator`, which provides more liberal behavior in that it defaults to coercing the other side of the expression into this type, thus applying special Python conversions above and beyond those needed by the DBAPI to both ides. It also provides the public method `TypeDecorator.coerce_compared_value()` which is intended for end-user customization of this behavior.

  attribute `sqlalchemy.dialects.postgresql.JSONB.`comparator_factory

    alias of `Comparator`

class sqlalchemy.dialects.postgresql.JSONPATH

  inherits from `sqlalchemy.dialects.postgresql.json.JSONPathType`

  JSON Path Type.

  This is usually required to cast literal values to json path when using json search like function, such as `jsonb_path_query_array` or `jsonb_path_exists`:

      stmt = sa.select(
          sa.func.jsonb_path_query_array(
              table.c.jsonb_col, cast("$.address.id", JSONPATH)
          )
      )

class sqlalchemy.dialects.postgresql.MACADDR

  inherits from `sqlalchemy.dialects.postgresql.types._NetworkAddressTypeMixin`, `sqlalchemy.types.TypeEngine`

class sqlalchemy.dialects.postgresql.MACADDR8

  inherits from `sqlalchemy.dialects.postgresql.types._NetworkAddressTypeMixin`, `sqlalchemy.types.TypeEngine`

class sqlalchemy.dialects.postgresql.MONEY

  inherits from `sqlalchemy.types.TypeEngine`

  Provide the PostgreSQL MONEY type.

  Depending on driver, result rows using this type may return a string value which includes currency symbols.

  For this reason, it may be preferable to provide conversion to a numerically-based currency datatype using `TypeDecorator`:

      import re
      import decimal
      from sqlalchemy import Dialect
      from sqlalchemy import TypeDecorator

      class NumericMoney(TypeDecorator):
          impl = MONEY

          def process_result_value(self, value: Any, dialect: Dialect) -> None:
              if value is not None:
                  # adjust this for the currency and numeric
                  m = re.match(r"\$([\d.]+)", value)
                  if m:
                      value = decimal.Decimal(m.group(1))
              return value

  Alternatively, the conversion may be applied as a CAST using the `TypeDecorator.column_expression()` method as follows:

      import decimal
      from sqlalchemy import cast
      from sqlalchemy import TypeDecorator

      class NumericMoney(TypeDecorator):
          impl = MONEY

          def column_expression(self, column: Any):
              return cast(column, Numeric())

  Added in version 1.2.

class sqlalchemy.dialects.postgresql.OID

  inherits from `sqlalchemy.types.TypeEngine`

  Provide the PostgreSQL OID type.

class sqlalchemy.dialects.postgresql.REAL

  inherits from `sqlalchemy.types.Float`

  The SQL REAL type.

  See also

  `Float` - documentation for the base type.

  method `sqlalchemy.dialects.postgresql.REAL.`__init__(precision: int | None = None, asdecimal: bool = False, decimal_return_scale: int | None = None)

    inherited from the `sqlalchemy.types.Float.__init__` method of `Float`

    Construct a Float.

    Parameters:

      - precision –

        the numeric precision for use in DDL `CREATE TABLE`. Backends should attempt to ensure this precision indicates a number of digits for the generic `Float` datatype.

        Note

        For the Oracle Database backend, the `Float.precision` parameter is not accepted when rendering DDL, as Oracle Database does not support float precision specified as a number of decimal places. Instead, use the Oracle Database-specific `FLOAT` datatype and specify the `FLOAT.binary_precision` parameter. This is new in version 2.0 of SQLAlchemy.

        To create a database agnostic `Float` that separately specifies binary precision for Oracle Database, use `TypeEngine.with_variant()` as follows:

            from sqlalchemy import Column
            from sqlalchemy import Float
            from sqlalchemy.dialects import oracle

            Column(
                "float_data",
                Float(5).with_variant(oracle.FLOAT(binary_precision=16), "oracle"),
            )

      - asdecimal – the same flag as that of `Numeric`, but defaults to `False`. Note that setting this flag to `True` results in floating point conversion.

      - decimal_return_scale – Default scale to use when converting from floats to Python decimals. Floating point values will typically be much longer due to decimal inaccuracy, and most floating point database types don’t have a notion of “scale”, so by default the float type looks for the first ten decimal places when converting. Specifying this value will override that length. Note that the MySQL float types, which do include “scale”, will use “scale” as the default for decimal_return_scale, if not otherwise specified.

class sqlalchemy.dialects.postgresql.REGCONFIG

  inherits from `sqlalchemy.types.TypeEngine`

  Provide the PostgreSQL REGCONFIG type.

  Added in version 2.0.0rc1.

class sqlalchemy.dialects.postgresql.REGCLASS

  inherits from `sqlalchemy.types.TypeEngine`

  Provide the PostgreSQL REGCLASS type.

  Added in version 1.2.7.

class sqlalchemy.dialects.postgresql.TIMESTAMP

  inherits from `sqlalchemy.types.TIMESTAMP`

  Provide the PostgreSQL TIMESTAMP type.

  Member Name | Description
  --- | ---
  __init__() | Construct a TIMESTAMP.

  method `sqlalchemy.dialects.postgresql.TIMESTAMP.`__init__(timezone: bool = False, precision: int | None = None) → None

    Construct a TIMESTAMP.

    Parameters:

      - timezone – boolean value if timezone present, default False

      - precision –

        optional integer precision value

        Added in version 1.4.

class sqlalchemy.dialects.postgresql.TIME

  inherits from `sqlalchemy.types.TIME`

  PostgreSQL TIME type.

  Member Name | Description
  --- | ---
  __init__() | Construct a TIME.

  method `sqlalchemy.dialects.postgresql.TIME.`__init__(timezone: bool = False, precision: int | None = None) → None

    Construct a TIME.

    Parameters:

      - timezone – boolean value if timezone present, default False

      - precision –

        optional integer precision value

        Added in version 1.4.

class sqlalchemy.dialects.postgresql.TSQUERY

  inherits from `sqlalchemy.types.TypeEngine`

  Provide the PostgreSQL TSQUERY type.

  Added in version 2.0.0rc1.

class sqlalchemy.dialects.postgresql.TSVECTOR

  inherits from `sqlalchemy.types.TypeEngine`

  The `TSVECTOR` type implements the PostgreSQL text search type TSVECTOR.

  It can be used to do full text queries on natural language documents.

  See also

  Full Text Search

class sqlalchemy.dialects.postgresql.UUID

  inherits from `sqlalchemy.types.Uuid`, `sqlalchemy.types.NativeForEmulated`

  Represent the SQL UUID type.

  This is the SQL-native form of the `Uuid` database agnostic datatype, and is backwards compatible with the previous PostgreSQL-only version of `UUID`.

  The `UUID` datatype only works on databases that have a SQL datatype named `UUID`. It will not function for backends which don’t have this exact-named type, including SQL Server. For backend-agnostic UUID values with native support, including for SQL Server’s `UNIQUEIDENTIFIER` datatype, use the `Uuid` datatype.

  Added in version 2.0.

  See also

  `Uuid`

  method `sqlalchemy.dialects.postgresql.UUID.`__init__(as_uuid: bool = True)

    Construct a `UUID` type.

    Parameters:

      as_uuid=True –

      if True, values will be interpreted as Python uuid objects, converting to/from string via the DBAPI.

class sqlalchemy.dialects.postgresql.INT4RANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractSingleRange`

  Represent the PostgreSQL INT4RANGE type.

class sqlalchemy.dialects.postgresql.INT8RANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractSingleRange`

  Represent the PostgreSQL INT8RANGE type.

class sqlalchemy.dialects.postgresql.NUMRANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractSingleRange`

  Represent the PostgreSQL NUMRANGE type.

class sqlalchemy.dialects.postgresql.DATERANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractSingleRange`

  Represent the PostgreSQL DATERANGE type.

class sqlalchemy.dialects.postgresql.TSRANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractSingleRange`

  Represent the PostgreSQL TSRANGE type.

class sqlalchemy.dialects.postgresql.TSTZRANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractSingleRange`

  Represent the PostgreSQL TSTZRANGE type.

class sqlalchemy.dialects.postgresql.INT4MULTIRANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractMultiRange`

  Represent the PostgreSQL INT4MULTIRANGE type.

class sqlalchemy.dialects.postgresql.INT8MULTIRANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractMultiRange`

  Represent the PostgreSQL INT8MULTIRANGE type.

class sqlalchemy.dialects.postgresql.NUMMULTIRANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractMultiRange`

  Represent the PostgreSQL NUMMULTIRANGE type.

class sqlalchemy.dialects.postgresql.DATEMULTIRANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractMultiRange`

  Represent the PostgreSQL DATEMULTIRANGE type.

class sqlalchemy.dialects.postgresql.TSMULTIRANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractMultiRange`

  Represent the PostgreSQL TSRANGE type.

class sqlalchemy.dialects.postgresql.TSTZMULTIRANGE

  inherits from `sqlalchemy.dialects.postgresql.ranges.AbstractMultiRange`

  Represent the PostgreSQL TSTZRANGE type.

class sqlalchemy.dialects.postgresql.MultiRange

  inherits from `builtins.list`, `typing.Generic`

  Represents a multirange sequence.

  This list subclass is an utility to allow automatic type inference of the proper multi-range SQL type depending on the single range values. This is useful when operating on literal multi-ranges:

      import sqlalchemy as sa
      from sqlalchemy.dialects.postgresql import MultiRange, Range

      value = literal(MultiRange([Range(2, 4)]))

      select(tbl).where(tbl.c.value.op("@")(MultiRange([Range(-3, 7)])))

  Added in version 2.0.26.

  See also

  - Use of a MultiRange sequence to infer the multirange type.

## PostgreSQL SQL Elements and Functions

Object Name | Description
--- | ---
aggregate_order_by | Represent a PostgreSQL aggregate order by expression.
All(other, arrexpr[, operator]) | A synonym for the ARRAY-level `Comparator.all()` method. See that method for details.
Any(other, arrexpr[, operator]) | A synonym for the ARRAY-level `Comparator.any()` method. See that method for details.
array | A PostgreSQL ARRAY literal.
array_agg(*arg, **kw) | PostgreSQL-specific form of `array_agg`, ensures return type is `ARRAY` and not the plain `ARRAY`, unless an explicit `type_` is passed.
hstore | Construct an hstore value within a SQL expression using the PostgreSQL `hstore()` function.
phraseto_tsquery | The PostgreSQL `phraseto_tsquery` SQL function.
plainto_tsquery | The PostgreSQL `plainto_tsquery` SQL function.
to_tsquery | The PostgreSQL `to_tsquery` SQL function.
to_tsvector | The PostgreSQL `to_tsvector` SQL function.
ts_headline | The PostgreSQL `ts_headline` SQL function.
websearch_to_tsquery | The PostgreSQL `websearch_to_tsquery` SQL function.

class sqlalchemy.dialects.postgresql.aggregate_order_by

  inherits from `sqlalchemy.sql.expression.ColumnElement`

  Represent a PostgreSQL aggregate order by expression.

  E.g.:

      from sqlalchemy.dialects.postgresql import aggregate_order_by

      expr = func.array_agg(aggregate_order_by(table.c.a, table.c.b.desc()))
      stmt = select(expr)

  would represent the expression:

      SELECT array_agg(a ORDER BY b DESC) FROM table;

  Similarly:

      expr = func.string_agg(
          table.c.a, aggregate_order_by(literal_column("','"), table.c.a)
      )
      stmt = select(expr)

  Would represent:

      SELECT string_agg(a, ',' ORDER BY a) FROM table;

  Changed in version 1.2.13: - the ORDER BY argument may be multiple terms

  See also

  `array_agg`

class sqlalchemy.dialects.postgresql.array

  inherits from `sqlalchemy.sql.expression.ExpressionClauseList`

  A PostgreSQL ARRAY literal.

  This is used to produce ARRAY literals in SQL expressions, e.g.:

      from sqlalchemy.dialects.postgresql import array
      from sqlalchemy.dialects import postgresql
      from sqlalchemy import select, func

      stmt = select(array([1, 2]) + array([3, 4, 5]))

      print(stmt.compile(dialect=postgresql.dialect()))

  Produces the SQL:

      SELECT ARRAY[%(param_1)s, %(param_2)s] ||
          ARRAY[%(param_3)s, %(param_4)s, %(param_5)s]) AS anon_1

  An instance of `array` will always have the datatype `ARRAY`. The “inner” type of the array is inferred from the values present, unless the `array.type_` keyword argument is passed:

      array(["foo", "bar"], type_=CHAR)

  When constructing an empty array, the `array.type_` argument is particularly important as PostgreSQL server typically requires a cast to be rendered for the inner type in order to render an empty array. SQLAlchemy’s compilation for the empty array will produce this cast so that:

      stmt = array([], type_=Integer)
      print(stmt.compile(dialect=postgresql.dialect()))

  Produces:

      ARRAY[]::INTEGER[]

  As required by PostgreSQL for empty arrays.

  Added in version 2.0.40: added support to render empty PostgreSQL array literals with a required cast.

  Multidimensional arrays are produced by nesting `array` constructs. The dimensionality of the final `ARRAY` type is calculated by recursively adding the dimensions of the inner `ARRAY` type:

      stmt = select(
          array(
              [array([1, 2]), array([3, 4]), array([column("q"), column("x")])]
          )
      )
      print(stmt.compile(dialect=postgresql.dialect()))

  Produces:

      SELECT ARRAY[
          ARRAY[%(param_1)s, %(param_2)s],
          ARRAY[%(param_3)s, %(param_4)s],
          ARRAY[q, x]
      ] AS anon_1

  Added in version 1.3.6: added support for multidimensional array literals

  See also

  `ARRAY`

  Member Name | Description
  --- | ---
  __init__() | Construct an ARRAY literal.

  method `sqlalchemy.dialects.postgresql.array.`__init__(clauses: Iterable[_T], *, type_: _TypeEngineArgument[_T] | None = None, **kw: typing_Any)

    Construct an ARRAY literal.

    Parameters:

      - clauses – iterable, such as a list, containing elements to be rendered in the array

      - type_ – optional type. If omitted, the type is inferred from the contents of the array.

function sqlalchemy.dialects.postgresql.array_agg(*arg, **kw)

  PostgreSQL-specific form of `array_agg`, ensures return type is `ARRAY` and not the plain `ARRAY`, unless an explicit `type_` is passed.

function sqlalchemy.dialects.postgresql.Any(other: typing_Any, arrexpr: _ColumnExpressionArgument[_T], operator: OperatorType = <built-in function eq>) → ColumnElement[bool]

  A synonym for the ARRAY-level `Comparator.any()` method. See that method for details.

function sqlalchemy.dialects.postgresql.All(other: typing_Any, arrexpr: _ColumnExpressionArgument[_T], operator: OperatorType = <built-in function eq>) → ColumnElement[bool]

  A synonym for the ARRAY-level `Comparator.all()` method. See that method for details.

class sqlalchemy.dialects.postgresql.hstore

  inherits from `sqlalchemy.sql.functions.GenericFunction`

  Construct an hstore value within a SQL expression using the PostgreSQL `hstore()` function.

  The `hstore` function accepts one or two arguments as described in the PostgreSQL documentation.

  E.g.:

      from sqlalchemy.dialects.postgresql import array, hstore

      select(hstore("key1", "value1"))

      select(
          hstore(
              array(["key1", "key2", "key3"]),
              array(["value1", "value2", "value3"]),
          )
      )

  See also

  `HSTORE` - the PostgreSQL `HSTORE` datatype.

  Member Name | Description
  --- | ---
  inherit_cache | Indicate if this `HasCacheKey` instance should make use of the cache key generation scheme used by its immediate superclass.
  type | alias of `HSTORE`

  attribute `sqlalchemy.dialects.postgresql.hstore.`inherit_cache: bool | None = True

    Indicate if this `HasCacheKey` instance should make use of the cache key generation scheme used by its immediate superclass.

    The attribute defaults to `None`, which indicates that a construct has not yet taken into account whether or not its appropriate for it to participate in caching; this is functionally equivalent to setting the value to `False`, except that a warning is also emitted.

    This flag can be set to `True` on a particular class, if the SQL that corresponds to the object does not change based on attributes which are local to this class, and not its superclass.

    See also

    Enabling Caching Support for Custom Constructs - General guideslines for setting the `HasCacheKey.inherit_cache` attribute for third-party or user defined SQL constructs.

  attribute `sqlalchemy.dialects.postgresql.hstore.`type

    alias of `HSTORE`

class sqlalchemy.dialects.postgresql.to_tsvector

  inherits from `sqlalchemy.dialects.postgresql.ext._regconfig_fn`

  The PostgreSQL `to_tsvector` SQL function.

  This function applies automatic casting of the REGCONFIG argument to use the `REGCONFIG` datatype automatically, and applies a return type of `TSVECTOR`.

  Assuming the PostgreSQL dialect has been imported, either by invoking `from sqlalchemy.dialects import postgresql`, or by creating a PostgreSQL engine using `create_engine("postgresql...")`, `to_tsvector` will be used automatically when invoking `sqlalchemy.func.to_tsvector()`, ensuring the correct argument and return type handlers are used at compile and execution time.

  Added in version 2.0.0rc1.

class sqlalchemy.dialects.postgresql.to_tsquery

  inherits from `sqlalchemy.dialects.postgresql.ext._regconfig_fn`

  The PostgreSQL `to_tsquery` SQL function.

  This function applies automatic casting of the REGCONFIG argument to use the `REGCONFIG` datatype automatically, and applies a return type of `TSQUERY`.

  Assuming the PostgreSQL dialect has been imported, either by invoking `from sqlalchemy.dialects import postgresql`, or by creating a PostgreSQL engine using `create_engine("postgresql...")`, `to_tsquery` will be used automatically when invoking `sqlalchemy.func.to_tsquery()`, ensuring the correct argument and return type handlers are used at compile and execution time.

  Added in version 2.0.0rc1.

class sqlalchemy.dialects.postgresql.plainto_tsquery

  inherits from `sqlalchemy.dialects.postgresql.ext._regconfig_fn`

  The PostgreSQL `plainto_tsquery` SQL function.

  This function applies automatic casting of the REGCONFIG argument to use the `REGCONFIG` datatype automatically, and applies a return type of `TSQUERY`.

  Assuming the PostgreSQL dialect has been imported, either by invoking `from sqlalchemy.dialects import postgresql`, or by creating a PostgreSQL engine using `create_engine("postgresql...")`, `plainto_tsquery` will be used automatically when invoking `sqlalchemy.func.plainto_tsquery()`, ensuring the correct argument and return type handlers are used at compile and execution time.

  Added in version 2.0.0rc1.

class sqlalchemy.dialects.postgresql.phraseto_tsquery

  inherits from `sqlalchemy.dialects.postgresql.ext._regconfig_fn`

  The PostgreSQL `phraseto_tsquery` SQL function.

  This function applies automatic casting of the REGCONFIG argument to use the `REGCONFIG` datatype automatically, and applies a return type of `TSQUERY`.

  Assuming the PostgreSQL dialect has been imported, either by invoking `from sqlalchemy.dialects import postgresql`, or by creating a PostgreSQL engine using `create_engine("postgresql...")`, `phraseto_tsquery` will be used automatically when invoking `sqlalchemy.func.phraseto_tsquery()`, ensuring the correct argument and return type handlers are used at compile and execution time.

  Added in version 2.0.0rc1.

class sqlalchemy.dialects.postgresql.websearch_to_tsquery

  inherits from `sqlalchemy.dialects.postgresql.ext._regconfig_fn`

  The PostgreSQL `websearch_to_tsquery` SQL function.

  This function applies automatic casting of the REGCONFIG argument to use the `REGCONFIG` datatype automatically, and applies a return type of `TSQUERY`.

  Assuming the PostgreSQL dialect has been imported, either by invoking `from sqlalchemy.dialects import postgresql`, or by creating a PostgreSQL engine using `create_engine("postgresql...")`, `websearch_to_tsquery` will be used automatically when invoking `sqlalchemy.func.websearch_to_tsquery()`, ensuring the correct argument and return type handlers are used at compile and execution time.

  Added in version 2.0.0rc1.

class sqlalchemy.dialects.postgresql.ts_headline

  inherits from `sqlalchemy.dialects.postgresql.ext._regconfig_fn`

  The PostgreSQL `ts_headline` SQL function.

  This function applies automatic casting of the REGCONFIG argument to use the `REGCONFIG` datatype automatically, and applies a return type of `TEXT`.

  Assuming the PostgreSQL dialect has been imported, either by invoking `from sqlalchemy.dialects import postgresql`, or by creating a PostgreSQL engine using `create_engine("postgresql...")`, `ts_headline` will be used automatically when invoking `sqlalchemy.func.ts_headline()`, ensuring the correct argument and return type handlers are used at compile and execution time.

  Added in version 2.0.0rc1.

## PostgreSQL Constraint Types

SQLAlchemy supports PostgreSQL EXCLUDE constraints via the `ExcludeConstraint` class:

Object Name | Description
--- | ---
ExcludeConstraint | A table-level EXCLUDE constraint.

class sqlalchemy.dialects.postgresql.ExcludeConstraint

  inherits from `sqlalchemy.schema.ColumnCollectionConstraint`

  A table-level EXCLUDE constraint.

  Defines an EXCLUDE constraint as described in the PostgreSQL documentation.

  Member Name | Description
  --- | ---
  __init__() | Create an `ExcludeConstraint` object.

  method `sqlalchemy.dialects.postgresql.ExcludeConstraint.`__init__(*elements: Tuple[_DDLColumnArgument, str], **kw: Any) → None

    Create an `ExcludeConstraint` object.

    E.g.:

        const = ExcludeConstraint(
            (Column("period"), "&&"),
            (Column("group"), "="),
            where=(Column("group") != "some group"),
            ops={"group": "my_operator_class"},
        )

    The constraint is normally embedded into the `Table` construct directly, or added later using `append_constraint()`:

        some_table = Table(
            "some_table",
            metadata,
            Column("id", Integer, primary_key=True),
            Column("period", TSRANGE()),
            Column("group", String),
        )

        some_table.append_constraint(
            ExcludeConstraint(
                (some_table.c.period, "&&"),
                (some_table.c.group, "="),
                where=some_table.c.group != "some group",
                name="some_table_excl_const",
                ops={"group": "my_operator_class"},
            )
        )

    The exclude constraint defined in this example requires the `btree_gist` extension, that can be created using the command `CREATE EXTENSION btree_gist;`.

    Parameters:

      - *elements –

        A sequence of two tuples of the form `(column, operator)` where “column” is either a `Column` object, or a SQL expression element (e.g. `func.int8range(table.from, table.to)`) or the name of a column as string, and “operator” is a string containing the operator to use (e.g. “&&” or “=”).

        In order to specify a column name when a `Column` object is not available, while ensuring that any necessary quoting rules take effect, an ad-hoc `Column` or `column()` object should be used. The `column` may also be a string SQL expression when passed as `literal_column()` or `text()`

      - name – Optional, the in-database name of this constraint.

      - deferrable – Optional bool. If set, emit DEFERRABLE or NOT DEFERRABLE when issuing DDL for this constraint.

      - initially – Optional string. If set, emit INITIALLY <value> when issuing DDL for this constraint.

      - using – Optional string. If set, emit USING <index_method> when issuing DDL for this constraint. Defaults to ‘gist’.

      - where – Optional SQL expression construct or literal SQL string. If set, emit WHERE <predicate> when issuing DDL for this constraint.

      - ops –

        Optional dictionary. Used to define operator classes for the elements; works the same way as that of the postgresql_ops parameter specified to the `Index` construct.

        Added in version 1.3.21.

        See also

        Operator Classes - general description of how PostgreSQL operator classes are specified.

For example:

    from sqlalchemy.dialects.postgresql import ExcludeConstraint, TSRANGE

    class RoomBooking(Base):
        __tablename__ = "room_booking"

        room = Column(Integer(), primary_key=True)
        during = Column(TSRANGE())

        __table_args__ = (ExcludeConstraint(("room", "="), ("during", "&&")),)

## PostgreSQL DML Constructs

Object Name | Description
--- | ---
insert(table) | Construct a PostgreSQL-specific variant `Insert` construct.
Insert | PostgreSQL-specific implementation of INSERT.

function sqlalchemy.dialects.postgresql.insert(table: _DMLTableArgument) → Insert

  Construct a PostgreSQL-specific variant `Insert` construct.

  The `sqlalchemy.dialects.postgresql.insert()` function creates a `sqlalchemy.dialects.postgresql.Insert`. This class is based on the dialect-agnostic `Insert` construct which may be constructed using the `insert()` function in SQLAlchemy Core.

  The `Insert` construct includes additional methods `Insert.on_conflict_do_update()`, `Insert.on_conflict_do_nothing()`.

class sqlalchemy.dialects.postgresql.Insert

  inherits from `sqlalchemy.sql.expression.Insert`

  PostgreSQL-specific implementation of INSERT.

  Adds methods for PG-specific syntaxes such as ON CONFLICT.

  The `Insert` object is created using the `sqlalchemy.dialects.postgresql.insert()` function.

  Member Name | Description
  --- | ---
  excluded | Provide the `excluded` namespace for an ON CONFLICT statement
  inherit_cache | Indicate if this `HasCacheKey` instance should make use of the cache key generation scheme used by its immediate superclass.
  on_conflict_do_nothing() | Specifies a DO NOTHING action for ON CONFLICT clause.
  on_conflict_do_update() | Specifies a DO UPDATE SET action for ON CONFLICT clause.

  attribute `sqlalchemy.dialects.postgresql.Insert.`excluded

    Provide the `excluded` namespace for an ON CONFLICT statement

    PG’s ON CONFLICT clause allows reference to the row that would be inserted, known as `excluded`. This attribute provides all columns in this row to be referenceable.

    Tip

    The `Insert.excluded` attribute is an instance of `ColumnCollection`, which provides an interface the same as that of the `Table.c` collection described at Accessing Tables and Columns. With this collection, ordinary names are accessible like attributes (e.g. `stmt.excluded.some_column`), but special names and dictionary method names should be accessed using indexed access, such as `stmt.excluded["column name"]` or `stmt.excluded["values"]`. See the docstring for `ColumnCollection` for further examples.

    See also

    INSERT…ON CONFLICT (Upsert) - example of how to use `Insert.excluded`

  attribute `sqlalchemy.dialects.postgresql.Insert.`inherit_cache: bool | None = False

    Indicate if this `HasCacheKey` instance should make use of the cache key generation scheme used by its immediate superclass.

    The attribute defaults to `None`, which indicates that a construct has not yet taken into account whether or not its appropriate for it to participate in caching; this is functionally equivalent to setting the value to `False`, except that a warning is also emitted.

    This flag can be set to `True` on a particular class, if the SQL that corresponds to the object does not change based on attributes which are local to this class, and not its superclass.

    See also

    Enabling Caching Support for Custom Constructs - General guideslines for setting the `HasCacheKey.inherit_cache` attribute for third-party or user defined SQL constructs.

  method `sqlalchemy.dialects.postgresql.Insert.`on_conflict_do_nothing(constraint: str | ColumnCollectionConstraint | Index | None = None, index_elements: Iterable[Column[Any] | str | DDLConstraintColumnRole] | None = None, index_where: WhereHavingRole | None = None) → Self

    Specifies a DO NOTHING action for ON CONFLICT clause.

    The `constraint` and `index_elements` arguments are optional, but only one of these can be specified.

    Parameters:

      - constraint – The name of a unique or exclusion constraint on the table, or the constraint object itself if it has a .name attribute.

      - index_elements – A sequence consisting of string column names, `Column` objects, or other column expression objects that will be used to infer a target index.

      - index_where – Additional WHERE criterion that can be used to infer a conditional target index.

    See also

    INSERT…ON CONFLICT (Upsert)

  method `sqlalchemy.dialects.postgresql.Insert.`on_conflict_do_update(constraint: str | ColumnCollectionConstraint | Index | None = None, index_elements: Iterable[Column[Any] | str | DDLConstraintColumnRole] | None = None, index_where: WhereHavingRole | None = None, set_: Mapping[Any, Any] | ColumnCollection[Any, Any] | None = None, where: WhereHavingRole | None = None) → Self

    Specifies a DO UPDATE SET action for ON CONFLICT clause.

    Either the `constraint` or `index_elements` argument is required, but only one of these can be specified.

    Parameters:

      - constraint – The name of a unique or exclusion constraint on the table, or the constraint object itself if it has a .name attribute.

      - index_elements – A sequence consisting of string column names, `Column` objects, or other column expression objects that will be used to infer a target index.

      - index_where – Additional WHERE criterion that can be used to infer a conditional target index.

      - set_ –

        A dictionary or other mapping object where the keys are either names of columns in the target table, or `Column` objects or other ORM-mapped columns matching that of the target table, and expressions or literals as values, specifying the `SET` actions to take.

        Added in version 1.4: The `Insert.on_conflict_do_update.set_` parameter supports `Column` objects from the target `Table` as keys.

        Warning

        This dictionary does not take into account Python-specified default UPDATE values or generation functions, e.g. those specified using `Column.onupdate`. These values will not be exercised for an ON CONFLICT style of UPDATE, unless they are manually specified in the `Insert.on_conflict_do_update.set_` dictionary.

      - where – Optional argument. An expression object representing a `WHERE` clause that restricts the rows affected by `DO UPDATE SET`. Rows not meeting the `WHERE` condition will not be updated (effectively a `DO NOTHING` for those rows).

    See also

    INSERT…ON CONFLICT (Upsert)

## psycopg2

Support for the PostgreSQL database via the psycopg2 driver.

### DBAPI

Documentation and download information (if applicable) for psycopg2 is available at: https://pypi.org/project/psycopg2/

### Connecting

Connect String:

    postgresql+psycopg2://user:password@host:port/dbname[?key=value&key=value...]

### psycopg2 Connect Arguments

Keyword arguments that are specific to the SQLAlchemy psycopg2 dialect may be passed to `create_engine()`, and include the following:

- `isolation_level`: This option, available for all PostgreSQL dialects, includes the `AUTOCOMMIT` isolation level when using the psycopg2 dialect. This option sets the default isolation level for the connection that is set immediately upon connection to the database before the connection is pooled. This option is generally superseded by the more modern `Connection.execution_options.isolation_level` execution option, detailed at Setting Transaction Isolation Levels including DBAPI Autocommit.

  See also

  Psycopg2 Transaction Isolation Level

  Setting Transaction Isolation Levels including DBAPI Autocommit

- `client_encoding`: sets the client encoding in a libpq-agnostic way, using psycopg2’s `set_client_encoding()` method.

  See also

  Unicode with Psycopg2

- `executemany_mode`, `executemany_batch_page_size`, `executemany_values_page_size`: Allows use of psycopg2 extensions for optimizing “executemany”-style queries. See the referenced section below for details.

  See also

  Psycopg2 Fast Execution Helpers

Tip

The above keyword arguments are dialect keyword arguments, meaning that they are passed as explicit keyword arguments to `create_engine()`:

    engine = create_engine(
        "postgresql+psycopg2://scott:tiger@localhost/test",
        isolation_level="SERIALIZABLE",
    )

These should not be confused with DBAPI connect arguments, which are passed as part of the `create_engine.connect_args` dictionary and/or are passed in the URL query string, as detailed in the section Custom DBAPI connect() arguments / on-connect routines.

### SSL Connections

The psycopg2 module has a connection argument named `sslmode` for controlling its behavior regarding secure (SSL) connections. The default is `sslmode=prefer`; it will attempt an SSL connection and if that fails it will fall back to an unencrypted connection. `sslmode=require` may be used to ensure that only secure connections are established. Consult the psycopg2 / libpq documentation for further options that are available.

Note that `sslmode` is specific to psycopg2 so it is included in the connection URI:

    engine = sa.create_engine(
        "postgresql+psycopg2://scott:tiger@192.168.0.199:5432/test?sslmode=require"
    )

### Unix Domain Connections

psycopg2 supports connecting via Unix domain connections. When the `host` portion of the URL is omitted, SQLAlchemy passes `None` to psycopg2, which specifies Unix-domain communication rather than TCP/IP communication:

    create_engine("postgresql+psycopg2://user:password@/dbname")

By default, the socket file used is to connect to a Unix-domain socket in `/tmp`, or whatever socket directory was specified when PostgreSQL was built. This value can be overridden by passing a pathname to psycopg2, using `host` as an additional keyword argument:

    create_engine(
        "postgresql+psycopg2://user:password@/dbname?host=/var/lib/postgresql"
    )

Warning

The format accepted here allows for a hostname in the main URL in addition to the “host” query string argument. When using this URL format, the initial host is silently ignored. That is, this URL:

    engine = create_engine(
        "postgresql+psycopg2://user:password@myhost1/dbname?host=myhost2"
    )

Above, the hostname `myhost1` is silently ignored and discarded. The host which is connected is the `myhost2` host.

This is to maintain some degree of compatibility with PostgreSQL’s own URL format which has been tested to behave the same way and for which tools like PifPaf hardcode two hostnames.

See also

PQconnectdbParams

### Specifying multiple fallback hosts

psycopg2 supports multiple connection points in the connection string. When the `host` parameter is used multiple times in the query section of the URL, SQLAlchemy will create a single string of the host and port information provided to make the connections. Tokens may consist of `host::port` or just `host`; in the latter case, the default port is selected by libpq. In the example below, three host connections are specified, for `HostA::PortA`, `HostB` connecting to the default port, and `HostC::PortC`:

    create_engine(
        "postgresql+psycopg2://user:password@/dbname?host=HostA:PortA&host=HostB&host=HostC:PortC"
    )

As an alternative, libpq query string format also may be used; this specifies `host` and `port` as single query string arguments with comma-separated lists - the default port can be chosen by indicating an empty value in the comma separated list:

    create_engine(
        "postgresql+psycopg2://user:password@/dbname?host=HostA,HostB,HostC&port=PortA,,PortC"
    )

With either URL style, connections to each host is attempted based on a configurable strategy, which may be configured using the libpq `target_session_attrs` parameter. Per libpq this defaults to `any` which indicates a connection to each host is then attempted until a connection is successful. Other strategies include `primary`, `prefer-standby`, etc. The complete list is documented by PostgreSQL at libpq connection strings.

For example, to indicate two hosts using the `primary` strategy:

    create_engine(
        "postgresql+psycopg2://user:password@/dbname?host=HostA:PortA&host=HostB&host=HostC:PortC&target_session_attrs=primary"
    )

Changed in version 1.4.40: Port specification in psycopg2 multiple host format is repaired, previously ports were not correctly interpreted in this context. libpq comma-separated format is also now supported.

Added in version 1.3.20: Support for multiple hosts in PostgreSQL connection string.

See also

libpq connection strings - please refer to this section in the libpq documentation for complete background on multiple host support.

### Empty DSN Connections / Environment Variable Connections

The psycopg2 DBAPI can connect to PostgreSQL by passing an empty DSN to the libpq client library, which by default indicates to connect to a localhost PostgreSQL database that is open for “trust” connections. This behavior can be further tailored using a particular set of environment variables which are prefixed with `PG_...`, which are consumed by `libpq` to take the place of any or all elements of the connection string.

For this form, the URL can be passed without any elements other than the initial scheme:

    engine = create_engine("postgresql+psycopg2://")

In the above form, a blank “dsn” string is passed to the `psycopg2.connect()` function which in turn represents an empty DSN passed to libpq.

Added in version 1.3.2: support for parameter-less connections with psycopg2.

See also

Environment Variables - PostgreSQL documentation on how to use `PG_...` environment variables for connections.

### Per-Statement/Connection Execution Options

The following DBAPI-specific options are respected when used with `Connection.execution_options()`, `Executable.execution_options()`, `Query.execution_options()`, in addition to those not specific to DBAPIs:

- `isolation_level` - Set the transaction isolation level for the lifespan of a `Connection` (can only be set on a connection, not a statement or query). See Psycopg2 Transaction Isolation Level.

- `stream_results` - Enable or disable usage of psycopg2 server side cursors - this feature makes use of “named” cursors in combination with special result handling methods so that result rows are not fully buffered. Defaults to False, meaning cursors are buffered by default.

- `max_row_buffer` - when using `stream_results`, an integer value that specifies the maximum number of rows to buffer at a time. This is interpreted by the `BufferedRowCursorResult`, and if omitted the buffer will grow to ultimately store 1000 rows at a time.

  Changed in version 1.4: The `max_row_buffer` size can now be greater than 1000, and the buffer will grow to that size.

### Psycopg2 Fast Execution Helpers

Modern versions of psycopg2 include a feature known as Fast Execution Helpers , which have been shown in benchmarking to improve psycopg2’s executemany() performance, primarily with INSERT statements, by at least an order of magnitude.

SQLAlchemy implements a native form of the “insert many values” handler that will rewrite a single-row INSERT statement to accommodate for many values at once within an extended VALUES clause; this handler is equivalent to psycopg2’s `execute_values()` handler; an overview of this feature and its configuration are at “Insert Many Values” Behavior for INSERT statements.

Added in version 2.0: Replaced psycopg2’s `execute_values()` fast execution helper with a native SQLAlchemy mechanism known as insertmanyvalues.

The psycopg2 dialect retains the ability to use the psycopg2-specific `execute_batch()` feature, although it is not expected that this is a widely used feature. The use of this extension may be enabled using the `executemany_mode` flag which may be passed to `create_engine()`:

    engine = create_engine(
        "postgresql+psycopg2://scott:tiger@host/dbname",
        executemany_mode="values_plus_batch",
    )

Possible options for `executemany_mode` include:

- `values_only` - this is the default value. SQLAlchemy’s native insertmanyvalues handler is used for qualifying INSERT statements, assuming `create_engine.use_insertmanyvalues` is left at its default value of `True`. This handler rewrites simple INSERT statements to include multiple VALUES clauses so that many parameter sets can be inserted with one statement.

- `'values_plus_batch'`- SQLAlchemy’s native insertmanyvalues handler is used for qualifying INSERT statements, assuming `create_engine.use_insertmanyvalues` is left at its default value of `True`. Then, psycopg2’s `execute_batch()` handler is used for qualifying UPDATE and DELETE statements when executed with multiple parameter sets. When using this mode, the `CursorResult.rowcount` attribute will not contain a value for executemany-style executions against UPDATE and DELETE statements.

Changed in version 2.0: Removed the `'batch'` and `'None'` options from psycopg2 `executemany_mode`. Control over batching for INSERT statements is now configured via the `create_engine.use_insertmanyvalues` engine-level parameter.

The term “qualifying statements” refers to the statement being executed being a Core `insert()`, `update()` or `delete()` construct, and not a plain textual SQL string or one constructed using `text()`. It also may not be a special “extension” statement such as an “ON CONFLICT” “upsert” statement. When using the ORM, all insert/update/delete statements used by the ORM flush process are qualifying.

The “page size” for the psycopg2 “batch” strategy can be affected by using the `executemany_batch_page_size` parameter, which defaults to 100.

For the “insertmanyvalues” feature, the page size can be controlled using the `create_engine.insertmanyvalues_page_size` parameter, which defaults to 1000. An example of modifying both parameters is below:

    engine = create_engine(
        "postgresql+psycopg2://scott:tiger@host/dbname",
        executemany_mode="values_plus_batch",
        insertmanyvalues_page_size=5000,
        executemany_batch_page_size=500,
    )

See also

“Insert Many Values” Behavior for INSERT statements - background on “insertmanyvalues”

Sending Multiple Parameters - General information on using the `Connection` object to execute statements in such a way as to make use of the DBAPI `.executemany()` method.

### Unicode with Psycopg2

The psycopg2 DBAPI driver supports Unicode data transparently.

The client character encoding can be controlled for the psycopg2 dialect in the following ways:

- For PostgreSQL 9.1 and above, the `client_encoding` parameter may be passed in the database URL; this parameter is consumed by the underlying `libpq` PostgreSQL client library:

      engine = create_engine(
          "postgresql+psycopg2://user:pass@host/dbname?client_encoding=utf8"
      )

  Alternatively, the above `client_encoding` value may be passed using `create_engine.connect_args` for programmatic establishment with `libpq`:

      engine = create_engine(
          "postgresql+psycopg2://user:pass@host/dbname",
          connect_args={"client_encoding": "utf8"},
      )

- For all PostgreSQL versions, psycopg2 supports a client-side encoding value that will be passed to database connections when they are first established. The SQLAlchemy psycopg2 dialect supports this using the `client_encoding` parameter passed to `create_engine()`:

      engine = create_engine(
          "postgresql+psycopg2://user:pass@host/dbname", client_encoding="utf8"
      )

  Tip

  The above `client_encoding` parameter admittedly is very similar in appearance to usage of the parameter within the `create_engine.connect_args` dictionary; the difference above is that the parameter is consumed by psycopg2 and is passed to the database connection using `SET client_encoding TO 'utf8'`; in the previously mentioned style, the parameter is instead passed through psycopg2 and consumed by the `libpq` library.

- A common way to set up client encoding with PostgreSQL databases is to ensure it is configured within the server-side postgresql.conf file; this is the recommended way to set encoding for a server that is consistently of one encoding in all databases:

      # postgresql.conf file

      # client_encoding = sql_ascii # actually, defaults to database
      # encoding
      client_encoding = utf8

### Transactions

The psycopg2 dialect fully supports SAVEPOINT and two-phase commit operations.

### Psycopg2 Transaction Isolation Level

As discussed in Transaction Isolation Level, all PostgreSQL dialects support setting of transaction isolation level both via the `isolation_level` parameter passed to `create_engine()` , as well as the `isolation_level` argument used by `Connection.execution_options()`. When using the psycopg2 dialect , these options make use of psycopg2’s `set_isolation_level()` connection method, rather than emitting a PostgreSQL directive; this is because psycopg2’s API-level setting is always emitted at the start of each transaction in any case.

The psycopg2 dialect supports these constants for isolation level:

- `READ COMMITTED`

- `READ UNCOMMITTED`

- `REPEATABLE READ`

- `SERIALIZABLE`

- `AUTOCOMMIT`

See also

Transaction Isolation Level

pg8000 Transaction Isolation Level

### NOTICE logging

The psycopg2 dialect will log PostgreSQL NOTICE messages via the `sqlalchemy.dialects.postgresql` logger. When this logger is set to the `logging.INFO` level, notice messages will be logged:

    import logging

    logging.getLogger("sqlalchemy.dialects.postgresql").setLevel(logging.INFO)

Above, it is assumed that logging is configured externally. If this is not the case, configuration such as `logging.basicConfig()` must be utilized:

    import logging

    logging.basicConfig()  # log messages to stdout
    logging.getLogger("sqlalchemy.dialects.postgresql").setLevel(logging.INFO)

See also

Logging HOWTO - on the python.org website

### HSTORE type

The `psycopg2` DBAPI includes an extension to natively handle marshalling of the HSTORE type. The SQLAlchemy psycopg2 dialect will enable this extension by default when psycopg2 version 2.4 or greater is used, and it is detected that the target database has the HSTORE type set up for use. In other words, when the dialect makes the first connection, a sequence like the following is performed:

1. Request the available HSTORE oids using `psycopg2.extras.HstoreAdapter.get_oids()`. If this function returns a list of HSTORE identifiers, we then determine that the `HSTORE` extension is present. This function is skipped if the version of psycopg2 installed is less than version 2.4.

2. If the `use_native_hstore` flag is at its default of `True`, and we’ve detected that `HSTORE` oids are available, the `psycopg2.extensions.register_hstore()` extension is invoked for all connections.

The `register_hstore()` extension has the effect of all Python dictionaries being accepted as parameters regardless of the type of target column in SQL. The dictionaries are converted by this extension into a textual HSTORE expression. If this behavior is not desired, disable the use of the hstore extension by setting `use_native_hstore` to `False` as follows:

    engine = create_engine(
        "postgresql+psycopg2://scott:tiger@localhost/test",
        use_native_hstore=False,
    )

The `HSTORE` type is still supported when the `psycopg2.extensions.register_hstore()` extension is not used. It merely means that the coercion between Python dictionaries and the HSTORE string format, on both the parameter side and the result side, will take place within SQLAlchemy’s own marshalling logic, and not that of `psycopg2` which may be more performant.

## psycopg

Support for the PostgreSQL database via the psycopg (a.k.a. psycopg 3) driver.

### DBAPI

Documentation and download information (if applicable) for psycopg (a.k.a. psycopg 3) is available at: https://pypi.org/project/psycopg/

### Connecting

Connect String:

    postgresql+psycopg://user:password@host:port/dbname[?key=value&key=value...]

`psycopg` is the package and module name for version 3 of the `psycopg` database driver, formerly known as `psycopg2`. This driver is different enough from its `psycopg2` predecessor that SQLAlchemy supports it via a totally separate dialect; support for `psycopg2` is expected to remain for as long as that package continues to function for modern Python versions, and also remains the default dialect for the `postgresql://` dialect series.

The SQLAlchemy `psycopg` dialect provides both a sync and an async implementation under the same dialect name. The proper version is selected depending on how the engine is created:

- calling `create_engine()` with `postgresql+psycopg://...` will automatically select the sync version, e.g.:

      from sqlalchemy import create_engine

      sync_engine = create_engine(
          "postgresql+psycopg://scott:tiger@localhost/test"
      )

- calling `create_async_engine()` with `postgresql+psycopg://...` will automatically select the async version, e.g.:

      from sqlalchemy.ext.asyncio import create_async_engine

      asyncio_engine = create_async_engine(
          "postgresql+psycopg://scott:tiger@localhost/test"
      )

The asyncio version of the dialect may also be specified explicitly using the `psycopg_async` suffix, as:

    from sqlalchemy.ext.asyncio import create_async_engine

    asyncio_engine = create_async_engine(
        "postgresql+psycopg_async://scott:tiger@localhost/test"
    )

See also

psycopg2 - The SQLAlchemy `psycopg` dialect shares most of its behavior with the `psycopg2` dialect. Further documentation is available there.

### Using psycopg Connection Pooling

The `psycopg` driver provides its own connection pool implementation that may be used in place of SQLAlchemy’s pooling functionality. This pool implementation provides support for fixed and dynamic pool sizes (including automatic downsizing for unused connections), connection health pre-checks, and support for both synchronous and asynchronous code environments.

Here is an example that uses the sync version of the pool, using `psycopg_pool >= 3.3` that introduces support for `close_returns=True`:

    import psycopg_pool
    from sqlalchemy import create_engine
    from sqlalchemy.pool import NullPool

    # Create a psycopg_pool connection pool
    my_pool = psycopg_pool.ConnectionPool(
        conninfo="postgresql://scott:tiger@localhost/test",
        close_returns=True,  # Return "closed" active connections to the pool
        # ... other pool parameters as desired ...
    )

    # Create an engine that uses the connection pool to get a connection
    engine = create_engine(
        url="postgresql+psycopg://",  # Only need the dialect now
        poolclass=NullPool,  # Disable SQLAlchemy's default connection pool
        creator=my_pool.getconn,  # Use Psycopg 3 connection pool to obtain connections
    )

Similarly an the async example:

    import psycopg_pool
    from sqlalchemy.ext.asyncio import create_async_engine
    from sqlalchemy.pool import NullPool

    async def define_engine():
        # Create a psycopg_pool connection pool
        my_pool = psycopg_pool.AsyncConnectionPool(
            conninfo="postgresql://scott:tiger@localhost/test",
            open=False,  # See comment below
            close_returns=True,  # Return "closed" active connections to the pool
            # ... other pool parameters as desired ...
        )

        # Must explicitly open AsyncConnectionPool outside constructor
        # https://www.psycopg.org/psycopg3/docs/api/pool.html#psycopg_pool.AsyncConnectionPool
        await my_pool.open()

        # Create an engine that uses the connection pool to get a connection
        engine = create_async_engine(
            url="postgresql+psycopg://",  # Only need the dialect now
            poolclass=NullPool,  # Disable SQLAlchemy's default connection pool
            async_creator=my_pool.getconn,  # Use Psycopg 3 connection pool to obtain connections
        )

        return engine, my_pool

The resulting engine may then be used normally. Internally, Psycopg 3 handles connection pooling:

    with engine.connect() as conn:
        print(conn.scalar(text("select 42")))

See also

Connection pools - the Psycopg 3 documentation for `psycopg_pool.ConnectionPool`.

Example for older version of psycopg_pool - An example about using the `psycopg_pool<3.3` that did not have the `close_returns`` parameter.

### Using a different Cursor class

One of the differences between `psycopg` and the older `psycopg2` is how bound parameters are handled: `psycopg2` would bind them client side, while `psycopg` by default will bind them server side.

It’s possible to configure `psycopg` to do client side binding by specifying the `cursor_factory` to be `ClientCursor` when creating the engine:

    from psycopg import ClientCursor

    client_side_engine = create_engine(
        "postgresql+psycopg://...",
        connect_args={"cursor_factory": ClientCursor},
    )

Similarly when using an async engine the `AsyncClientCursor` can be specified:

    from psycopg import AsyncClientCursor

    client_side_engine = create_async_engine(
        "postgresql+psycopg://...",
        connect_args={"cursor_factory": AsyncClientCursor},
    )

See also

Client-side-binding cursors

## pg8000

Support for the PostgreSQL database via the pg8000 driver.

### DBAPI

Documentation and download information (if applicable) for pg8000 is available at: https://pypi.org/project/pg8000/

### Connecting

Connect String:

    postgresql+pg8000://user:password@host:port/dbname[?key=value&key=value...]

Changed in version 1.4: The pg8000 dialect has been updated for version 1.16.6 and higher, and is again part of SQLAlchemy’s continuous integration with full feature support.

### Unicode

pg8000 will encode / decode string values between it and the server using the PostgreSQL `client_encoding` parameter; by default this is the value in the `postgresql.conf` file, which often defaults to `SQL_ASCII`. Typically, this can be changed to `utf-8`, as a more useful default:

    # client_encoding = sql_ascii # actually, defaults to database encoding
    client_encoding = utf8

The `client_encoding` can be overridden for a session by executing the SQL:

    SET CLIENT_ENCODING TO 'utf8';

SQLAlchemy will execute this SQL on all new connections based on the value passed to `create_engine()` using the `client_encoding` parameter:

    engine = create_engine(
        "postgresql+pg8000://user:pass@host/dbname", client_encoding="utf8"
    )

### SSL Connections

pg8000 accepts a Python `SSLContext` object which may be specified using the `create_engine.connect_args` dictionary:

    import ssl

    ssl_context = ssl.create_default_context()
    engine = sa.create_engine(
        "postgresql+pg8000://scott:tiger@192.168.0.199/test",
        connect_args={"ssl_context": ssl_context},
    )

If the server uses an automatically-generated certificate that is self-signed or does not match the host name (as seen from the client), it may also be necessary to disable hostname checking:

    import ssl

    ssl_context = ssl.create_default_context()
    ssl_context.check_hostname = False
    ssl_context.verify_mode = ssl.CERT_NONE
    engine = sa.create_engine(
        "postgresql+pg8000://scott:tiger@192.168.0.199/test",
        connect_args={"ssl_context": ssl_context},
    )

### pg8000 Transaction Isolation Level

The pg8000 dialect offers the same isolation level settings as that of the psycopg2 dialect:

- `READ COMMITTED`

- `READ UNCOMMITTED`

- `REPEATABLE READ`

- `SERIALIZABLE`

- `AUTOCOMMIT`

See also

Transaction Isolation Level

Psycopg2 Transaction Isolation Level

## asyncpg

Support for the PostgreSQL database via the asyncpg driver.

### DBAPI

Documentation and download information (if applicable) for asyncpg is available at: https://magicstack.github.io/asyncpg/

### Connecting

Connect String:

    postgresql+asyncpg://user:password@host:port/dbname[?key=value&key=value...]

The asyncpg dialect is SQLAlchemy’s first Python asyncio dialect.

Using a special asyncio mediation layer, the asyncpg dialect is usable as the backend for the SQLAlchemy asyncio extension package.

This dialect should normally be used only with the `create_async_engine()` engine creation function:

    from sqlalchemy.ext.asyncio import create_async_engine

    engine = create_async_engine(
        "postgresql+asyncpg://user:pass@hostname/dbname"
    )

Added in version 1.4.

Note

By default asyncpg does not decode the `json` and `jsonb` types and returns them as strings. SQLAlchemy sets default type decoder for `json` and `jsonb` types using the python builtin `json.loads` function. The json implementation used can be changed by setting the attribute `json_deserializer` when creating the engine with `create_engine()` or `create_async_engine()`.

### Multihost Connections

The asyncpg dialect features support for multiple fallback hosts in the same way as that of the psycopg2 and psycopg dialects. The syntax is the same, using `host=<host>:<port>` combinations as additional query string arguments; however, there is no default port, so all hosts must have a complete port number present, otherwise an exception is raised:

    engine = create_async_engine(
        "postgresql+asyncpg://user:password@/dbname?host=HostA:5432&host=HostB:5432&host=HostC:5432"
    )

For complete background on this syntax, see Specifying multiple fallback hosts.

Added in version 2.0.18.

See also

Specifying multiple fallback hosts

### Prepared Statement Cache

The asyncpg SQLAlchemy dialect makes use of `asyncpg.connection.prepare()` for all statements. The prepared statement objects are cached after construction which appears to grant a 10% or more performance improvement for statement invocation. The cache is on a per-DBAPI connection basis, which means that the primary storage for prepared statements is within DBAPI connections pooled within the connection pool. The size of this cache defaults to 100 statements per DBAPI connection and may be adjusted using the `prepared_statement_cache_size` DBAPI argument (note that while this argument is implemented by SQLAlchemy, it is part of the DBAPI emulation portion of the asyncpg dialect, therefore is handled as a DBAPI argument, not a dialect argument):

    engine = create_async_engine(
        "postgresql+asyncpg://user:pass@hostname/dbname?prepared_statement_cache_size=500"
    )

To disable the prepared statement cache, use a value of zero:

    engine = create_async_engine(
        "postgresql+asyncpg://user:pass@hostname/dbname?prepared_statement_cache_size=0"
    )

Added in version 1.4.0b2: Added `prepared_statement_cache_size` for asyncpg.

Warning

The `asyncpg` database driver necessarily uses caches for PostgreSQL type OIDs, which become stale when custom PostgreSQL datatypes such as `ENUM` objects are changed via DDL operations. Additionally, prepared statements themselves which are optionally cached by SQLAlchemy’s driver as described above may also become “stale” when DDL has been emitted to the PostgreSQL database which modifies the tables or other objects involved in a particular prepared statement.

The SQLAlchemy asyncpg dialect will invalidate these caches within its local process when statements that represent DDL are emitted on a local connection, but this is only controllable within a single Python process / database engine. If DDL changes are made from other database engines and/or processes, a running application may encounter asyncpg exceptions `InvalidCachedStatementError` and/or `InternalServerError("cache lookup failed for type <oid>")` if it refers to pooled database connections which operated upon the previous structures. The SQLAlchemy asyncpg dialect will recover from these error cases when the driver raises these exceptions by clearing its internal caches as well as those of the asyncpg driver in response to them, but cannot prevent them from being raised in the first place if the cached prepared statement or asyncpg type caches have gone stale, nor can it retry the statement as the PostgreSQL transaction is invalidated when these errors occur.

### Prepared Statement Name with PGBouncer

By default, asyncpg enumerates prepared statements in numeric order, which can lead to errors if a name has already been taken for another prepared statement. This issue can arise if your application uses database proxies such as PgBouncer to handle connections. One possible workaround is to use dynamic prepared statement names, which asyncpg now supports through an optional `name` value for the statement name. This allows you to generate your own unique names that won’t conflict with existing ones. To achieve this, you can provide a function that will be called every time a prepared statement is prepared:

    from uuid import uuid4

    engine = create_async_engine(
        "postgresql+asyncpg://user:pass@somepgbouncer/dbname",
        poolclass=NullPool,
        connect_args={
            "prepared_statement_name_func": lambda: f"__asyncpg_{uuid4()}__",
        },
    )

See also

https://github.com/MagicStack/asyncpg/issues/837

https://github.com/sqlalchemy/sqlalchemy/issues/6467

Warning

When using PGBouncer, to prevent a buildup of useless prepared statements in your application, it’s important to use the `NullPool` pool class, and to configure PgBouncer to use DISCARD when returning connections. The DISCARD command is used to release resources held by the db connection, including prepared statements. Without proper setup, prepared statements can accumulate quickly and cause performance issues.

### Disabling the PostgreSQL JIT to improve ENUM datatype handling

Asyncpg has an issue when using PostgreSQL ENUM datatypes, where upon the creation of new database connections, an expensive query may be emitted in order to retrieve metadata regarding custom types which has been shown to negatively affect performance. To mitigate this issue, the PostgreSQL “jit” setting may be disabled from the client using this setting passed to `create_async_engine()`:

    engine = create_async_engine(
        "postgresql+asyncpg://user:password@localhost/tmp",
        connect_args={"server_settings": {"jit": "off"}},
    )

See also

https://github.com/MagicStack/asyncpg/issues/727

## psycopg2cffi

Support for the PostgreSQL database via the psycopg2cffi driver.

### DBAPI

Documentation and download information (if applicable) for psycopg2cffi is available at: https://pypi.org/project/psycopg2cffi/

### Connecting

Connect String:

    postgresql+psycopg2cffi://user:password@host:port/dbname[?key=value&key=value...]

`psycopg2cffi` is an adaptation of `psycopg2`, using CFFI for the C layer. This makes it suitable for use in e.g. PyPy. Documentation is as per `psycopg2`.

See also

`sqlalchemy.dialects.postgresql.psycopg2`