## How do I do a database query?

### I just want an array of the rows…

Use the `Database#execute` method. If you don’t give it a block, it will return an array of all the rows:

```ruby require ‘sqlite3’

db = SQLite3::Database.new( “test.db” ) rows = db.execute( “select * from test” ) ```

### I’d like to use a block to iterate through the rows…

Use the `Database#execute` method. If you give it a block, each row of the result will be yielded to the block:

```ruby require ‘sqlite3’

db = SQLite3::Database.new( “test.db” ) db.execute( “select * from test” ) do |row| … end ```

### I need to get the column names as well as the rows…

Use the `Database#execute2` method. This works just like `Database#execute`; if you don’t give it a block, it returns an array of rows; otherwise, it will yield each row to the block. However, the first row returned is always an array of the column names from the query:

```ruby require ‘sqlite3’

db = SQLite3::Database.new( “test.db” ) columns, *rows = db.execute2( “select * from test” )

# or use a block:

columns = nil db.execute2( “select * from test” ) do |row| if columns.nil? columns = row else # process row end end ```

### I just want the first row of the result set…

Easy. Just call `Database#get_first_row`:

`ruby row = db.get_first_row( "select * from table" )`

This also supports bind variables, just like `Database#execute` and friends.

### I just want the first value of the first row of the result set…

Also easy. Just call `Database#get_first_value`:

`ruby count = db.get_first_value( "select count(*) from table" )`

This also supports bind variables, just like `Database#execute` and friends.

## How do I prepare a statement for repeated execution?

If the same statement is going to be executed repeatedly, you can speed things up a bit by preparing the statement. You do this via the `Database#prepare` method. It returns a `Statement` object, and you can then invoke `#execute` on that to get the `ResultSet`:

```ruby stmt = db.prepare( “select * from person” )

1000.times do stmt.execute do |result| … end end

stmt.close

# or, use a block

db.prepare( “select * from person” ) do |stmt| 1000.times do stmt.execute do |result| … end end end ```

This is made more useful by the ability to bind variables to placeholders via the `Statement#bind_param` and `Statement#bind_params` methods. (See the next FAQ for details.)

## How do I use placeholders in an SQL statement?

Placeholders in an SQL statement take any of the following formats:

- `?`
- `?_nnn_`
- `:_word_`

Where n is an integer, and word is an alpha-numeric identifier (or number). When the placeholder is associated with a number, that number identifies the index of the bind variable to replace it with. When it is an identifier, it identifies the name of the corresponding bind variable. (In the instance of the first format–a single question mark–the placeholder is assigned a number one greater than the last index used, or 1 if it is the first.)

For example, here is a query using these placeholder formats:

`sql select * from table where ( c = ?2 or c = ? ) and d = :name and e = :1`

This defines 5 different placeholders: 1, 2, 3, and “name”.

You replace these placeholders by binding them to values. This can be accomplished in a variety of ways.

The `Database#execute`, and `Database#execute2` methods all accept additional arguments following the SQL statement. These arguments are assumed to be bind parameters, and they are bound (positionally) to their corresponding placeholders:

`ruby db.execute( "select * from table where a = ? and b = ?", "hello", "world" )`

The above would replace the first question mark with ‘hello’ and the second with ‘world’. If the placeholders have an explicit index given, they will be replaced with the bind parameter at that index (1-based).

If a Hash is given as a bind parameter, then its key/value pairs are bound to the placeholders. This is how you bind by name:

`ruby db.execute( "select * from table where a = :name and b = :value", "name" => "bob", "value" => "priceless" )`

You can also bind explicitly using the `Statement` object itself. Just pass additional parameters to the `Statement#execute` statement:

`ruby db.prepare( "select * from table where a = :name and b = ?" ) do |stmt| stmt.execute "value", "name" => "bob" end`

Or do a `Database#prepare` to get the `Statement`, and then use either `Statement#bind_param` or `Statement#bind_params`:

```ruby stmt = db.prepare( “select * from table where a = :name and b = ?” )

stmt.bind_param( “name”, “bob” ) stmt.bind_param( 1, “value” )

# or

stmt.bind_params( “value”, “name” => “bob” ) ```

## How do I discover metadata about a query?

If you ever want to know the names or types of the columns in a result set, you can do it in several ways.

The first way is to ask the row object itself. Each row will have a property “fields” that returns an array of the column names. The row will also have a property “types” that returns an array of the column types:

`ruby rows = db.execute( "select * from table" ) p rows[0].fields p rows[0].types`

Obviously, this approach requires you to execute a statement that actually returns data. If you don’t know if the statement will return any rows, but you still need the metadata, you can use `Database#query` and ask the `ResultSet` object itself:

`ruby db.query( "select * from table" ) do |result| p result.columns p result.types ... end`

Lastly, you can use `Database#prepare` and ask the `Statement` object what the metadata are:

`ruby stmt = db.prepare( "select * from table" ) p stmt.columns p stmt.types`

## I’d like the rows to be indexible by column name.

By default, each row from a query is returned as an `Array` of values. This means that you can only obtain values by their index. Sometimes, however, you would like to obtain values by their column name.

The first way to do this is to set the Database property `results_as_hash` to true. If you do this, then all rows will be returned as Hash objects, with the column names as the keys. (In this case, the `fields` property is unavailable on the row, although the “types” property remains.)

`ruby db.results_as_hash = true db.execute( "select * from table" ) do |row| p row['column1'] p row['column2'] end`

The other way is to use Ara Howard’s `ArrayFields` module. Just `require "arrayfields"`, and all of your rows will be indexable by column name, even though they are still arrays!

```ruby require ‘arrayfields’

… db.execute( “select * from table” ) do |row| p row[0] == row[‘column1’] p row[1] == row[‘column2’] end ```

## I’d like the values from a query to be the correct types, instead of String.

You can turn on “type translation” by setting `Database#type_translation` to true:

`ruby db.type_translation = true db.execute( "select * from table" ) do |row| p row end`

By doing this, each return value for each row will be translated to its correct type, based on its declared column type.

You can even declare your own translation routines, if (for example) you are using an SQL type that is not handled by default:

```ruby # assume “objects” table has the following schema: # create table objects ( # name varchar2(20), # thing object # )

db.type_translation = true db.translator.add_translator( “object” ) do |type, value| db.decode( value ) end

h = { :one=>:two, “three”=>”four”, 5=>6 } dump = db.encode( h )

db.execute( “insert into objects values ( ?, ? )”, “bob”, dump )

obj = db.get_first_value( “select thing from objects where name=’bob’” ) p obj == h ```

## How do I insert binary data into the database?

Use blobs. Blobs are new features of SQLite3. You have to use bind variables to make it work:

`ruby db.execute( "insert into foo ( ?, ? )", SQLite3::Blob.new( "\0\1\2\3\4\5" ), SQLite3::Blob.new( "a\0b\0c\0d ) )`

The blob values must be indicated explicitly by binding each parameter to a value of type `SQLite3::Blob`.

## How do I do a DDL (insert, update, delete) statement?

You can actually do inserts, updates, and deletes in exactly the same way as selects, but in general the `Database#execute` method will be most convenient:

`ruby db.execute( "insert into table values ( ?, ? )", *bind_vars )`

## How do I execute multiple statements in a single string?

The standard query methods (`Database#execute`, `Database#execute2`, `Database#query`, and `Statement#execute`) will only execute the first statement in the string that is given to them. Thus, if you have a string with multiple SQL statements, each separated by a string, you can’t use those methods to execute them all at once.

Instead, use `Database#execute_batch`:

```ruby sql = «SQL create table the_table ( a varchar2(30), b varchar2(30) );

    insert into the_table values ( 'one', 'two' );
    insert into the_table values ( 'three', 'four' );
    insert into the_table values ( 'five', 'six' );   SQL

db.execute_batch( sql ) ```

Unlike the other query methods, `Database#execute_batch` accepts no block. It will also only ever return `nil`. Thus, it is really only suitable for batch processing of DDL statements.

## How do I begin/end a transaction

Use `Database#transaction` to start a transaction. If you give it a block, the block will be automatically committed at the end of the block, unless an exception was raised, in which case the transaction will be rolled back. (Never explicitly call `Database#commit` or `Database#rollback` inside of a transaction block–you’ll get errors when the block terminates!)

`ruby database.transaction do |db| db.execute( "insert into table values ( 'a', 'b', 'c' )" ) ... end`

Alternatively, if you don’t give a block to `Database#transaction`, the transaction remains open until you explicitly call `Database#commit` or `Database#rollback`.

`ruby db.transaction db.execute( "insert into table values ( 'a', 'b', 'c' )" ) db.commit`

Note that SQLite does not allow nested transactions, so you’ll get errors if you try to open a new transaction while one is already active. Use `Database#transaction_active?` to determine whether a transaction is active or not.

## How do I discover metadata about a table/index?

## How do I do tweak database settings?