Query Builder Class
*******************

CodeIgniter gives you access to a Query Builder class. This pattern
allows information to be retrieved, inserted, and updated in your
database with minimal scripting. In some cases only one or two lines
of code are necessary to perform a database action. CodeIgniter does
not require that each database table be its own class file. It instead
provides a more simplified interface.

Beyond simplicity, a major benefit to using the Query Builder features
is that it allows you to create database independent applications,
since the query syntax is generated by each database adapter. It also
allows for safer queries, since the values are escaped automatically
by the system.

Note:

  If you intend to write your own queries you can disable this class
  in your database config file, allowing the core database library and
  adapter to utilize fewer resources.

* Selecting Data

* Looking for Specific Data

* Looking for Similar Data

* Ordering results

* Limiting or Counting Results

* Query grouping

* Inserting Data

* Updating Data

* Deleting Data

* Method Chaining

* Query Builder Caching

* Resetting Query Builder

* Class Reference


Selecting Data
==============

The following functions allow you to build SQL **SELECT** statements.

**$this->db->get()**

Runs the selection query and returns the result. Can be used by itself
to retrieve all records from a table:

   $query = $this->db->get('mytable');  // Produces: SELECT * FROM mytable

The second and third parameters enable you to set a limit and offset
clause:

   $query = $this->db->get('mytable', 10, 20);

   // Executes: SELECT * FROM mytable LIMIT 20, 10
   // (in MySQL. Other databases have slightly different syntax)

You’ll notice that the above function is assigned to a variable named
$query, which can be used to show the results:

   $query = $this->db->get('mytable');

   foreach ($query->result() as $row)
   {
           echo $row->title;
   }

Please visit the result functions page for a full discussion regarding
result generation.

**$this->db->get_compiled_select()**

Compiles the selection query just like **$this->db->get()** but does
not *run* the query. This method simply returns the SQL query as a
string.

Example:

   $sql = $this->db->get_compiled_select('mytable');
   echo $sql;

   // Prints string: SELECT * FROM mytable

The second parameter enables you to set whether or not the query
builder query will be reset (by default it will be reset, just like
when using *$this->db->get()*):

   echo $this->db->limit(10,20)->get_compiled_select('mytable', FALSE);

   // Prints string: SELECT * FROM mytable LIMIT 20, 10
   // (in MySQL. Other databases have slightly different syntax)

   echo $this->db->select('title, content, date')->get_compiled_select();

   // Prints string: SELECT title, content, date FROM mytable LIMIT 20, 10

The key thing to notice in the above example is that the second query
did not utilize **$this->db->from()** and did not pass a table name
into the first parameter. The reason for this outcome is because the
query has not been executed using **$this->db->get()** which resets
values or reset directly using **$this->db->reset_query()**.

**$this->db->get_where()**

Identical to the above function except that it permits you to add a
“where” clause in the second parameter, instead of using the
db->where() function:

   $query = $this->db->get_where('mytable', array('id' => $id), $limit, $offset);

Please read the about the where function below for more information.

Note:

  get_where() was formerly known as getwhere(), which has been removed

**$this->db->select()**

Permits you to write the SELECT portion of your query:

   $this->db->select('title, content, date');
   $query = $this->db->get('mytable');

   // Executes: SELECT title, content, date FROM mytable

Note:

  If you are selecting all (*) from a table you do not need to use
  this function. When omitted, CodeIgniter assumes that you wish to
  select all fields and automatically adds ‘SELECT *’.

"$this->db->select()" accepts an optional second parameter. If you set
it to FALSE, CodeIgniter will not try to protect your field or table
names. This is useful if you need a compound select statement where
automatic escaping of fields may break them.

   $this->db->select('(SELECT SUM(payments.amount) FROM payments WHERE payments.invoice_id=4) AS amount_paid', FALSE);
   $query = $this->db->get('mytable');

**$this->db->select_max()**

Writes a "SELECT MAX(field)" portion for your query. You can
optionally include a second parameter to rename the resulting field.

   $this->db->select_max('age');
   $query = $this->db->get('members');  // Produces: SELECT MAX(age) as age FROM members

   $this->db->select_max('age', 'member_age');
   $query = $this->db->get('members'); // Produces: SELECT MAX(age) as member_age FROM members

**$this->db->select_min()**

Writes a “SELECT MIN(field)” portion for your query. As with
select_max(), You can optionally include a second parameter to rename
the resulting field.

   $this->db->select_min('age');
   $query = $this->db->get('members'); // Produces: SELECT MIN(age) as age FROM members

**$this->db->select_avg()**

Writes a “SELECT AVG(field)” portion for your query. As with
select_max(), You can optionally include a second parameter to rename
the resulting field.

   $this->db->select_avg('age');
   $query = $this->db->get('members'); // Produces: SELECT AVG(age) as age FROM members

**$this->db->select_sum()**

Writes a “SELECT SUM(field)” portion for your query. As with
select_max(), You can optionally include a second parameter to rename
the resulting field.

   $this->db->select_sum('age');
   $query = $this->db->get('members'); // Produces: SELECT SUM(age) as age FROM members

**$this->db->from()**

Permits you to write the FROM portion of your query:

   $this->db->select('title, content, date');
   $this->db->from('mytable');
   $query = $this->db->get();  // Produces: SELECT title, content, date FROM mytable

Note:

  As shown earlier, the FROM portion of your query can be specified in
  the $this->db->get() function, so use whichever method you prefer.

**$this->db->join()**

Permits you to write the JOIN portion of your query:

   $this->db->select('*');
   $this->db->from('blogs');
   $this->db->join('comments', 'comments.id = blogs.id');
   $query = $this->db->get();

   // Produces:
   // SELECT * FROM blogs JOIN comments ON comments.id = blogs.id

Multiple function calls can be made if you need several joins in one
query.

If you need a specific type of JOIN you can specify it via the third
parameter of the function. Options are: left, right, outer, inner,
left outer, right outer and full outer.

   $this->db->join('comments', 'comments.id = blogs.id', 'left');
   // Produces: LEFT JOIN comments ON comments.id = blogs.id


Looking for Specific Data
=========================

**$this->db->where()**

This function enables you to set **WHERE** clauses using one of four
methods:

Note:

  All values passed to this function are escaped automatically,
  producing safer queries.

1. **Simple key/value method:**

         $this->db->where('name', $name); // Produces: WHERE name = 'Joe'

      Notice that the equal sign is added for you.

      If you use multiple function calls they will be chained together
      with AND between them:

         $this->db->where('name', $name);
         $this->db->where('title', $title);
         $this->db->where('status', $status);
         // WHERE name = 'Joe' AND title = 'boss' AND status = 'active'

2. **Custom key/value method:**

      You can include an operator in the first parameter in order to
      control the comparison:

         $this->db->where('name !=', $name);
         $this->db->where('id <', $id); // Produces: WHERE name != 'Joe' AND id < 45

3. **Associative array method:**

         $array = array('name' => $name, 'title' => $title, 'status' => $status);
         $this->db->where($array);
         // Produces: WHERE name = 'Joe' AND title = 'boss' AND status = 'active'

      You can include your own operators using this method as well:

         $array = array('name !=' => $name, 'id <' => $id, 'date >' => $date);
         $this->db->where($array);

4. **Custom string:**
      You can write your own clauses manually:

         $where = "name='Joe' AND status='boss' OR status='active'";
         $this->db->where($where);

"$this->db->where()" accepts an optional third parameter. If you set
it to FALSE, CodeIgniter will not try to protect your field or table
names.

   $this->db->where('MATCH (field) AGAINST ("value")', NULL, FALSE);

**$this->db->or_where()**

This function is identical to the one above, except that multiple
instances are joined by OR:

   $this->db->where('name !=', $name);
   $this->db->or_where('id >', $id);  // Produces: WHERE name != 'Joe' OR id > 50

Note:

  or_where() was formerly known as orwhere(), which has been removed.

**$this->db->where_in()**

Generates a WHERE field IN (‘item’, ‘item’) SQL query joined with AND
if appropriate

   $names = array('Frank', 'Todd', 'James');
   $this->db->where_in('username', $names);
   // Produces: WHERE username IN ('Frank', 'Todd', 'James')

**$this->db->or_where_in()**

Generates a WHERE field IN (‘item’, ‘item’) SQL query joined with OR
if appropriate

   $names = array('Frank', 'Todd', 'James');
   $this->db->or_where_in('username', $names);
   // Produces: OR username IN ('Frank', 'Todd', 'James')

**$this->db->where_not_in()**

Generates a WHERE field NOT IN (‘item’, ‘item’) SQL query joined with
AND if appropriate

   $names = array('Frank', 'Todd', 'James');
   $this->db->where_not_in('username', $names);
   // Produces: WHERE username NOT IN ('Frank', 'Todd', 'James')

**$this->db->or_where_not_in()**

Generates a WHERE field NOT IN (‘item’, ‘item’) SQL query joined with
OR if appropriate

   $names = array('Frank', 'Todd', 'James');
   $this->db->or_where_not_in('username', $names);
   // Produces: OR username NOT IN ('Frank', 'Todd', 'James')


Looking for Similar Data
========================

**$this->db->like()**

This method enables you to generate **LIKE** clauses, useful for doing
searches.

Note:

  All values passed to this method are escaped automatically.

1. **Simple key/value method:**

         $this->db->like('title', 'match');
         // Produces: WHERE `title` LIKE '%match%' ESCAPE '!'

      If you use multiple method calls they will be chained together
      with AND between them:

         $this->db->like('title', 'match');
         $this->db->like('body', 'match');
         // WHERE `title` LIKE '%match%' ESCAPE '!' AND  `body` LIKE '%match% ESCAPE '!'

      If you want to control where the wildcard (%) is placed, you can
      use an optional third argument. Your options are ‘before’,
      ‘after’, ‘none’ and ‘both’ (which is the default).

         $this->db->like('title', 'match', 'before');    // Produces: WHERE `title` LIKE '%match' ESCAPE '!'
         $this->db->like('title', 'match', 'after');     // Produces: WHERE `title` LIKE 'match%' ESCAPE '!'
         $this->db->like('title', 'match', 'none');      // Produces: WHERE `title` LIKE 'match' ESCAPE '!'
         $this->db->like('title', 'match', 'both');      // Produces: WHERE `title` LIKE '%match%' ESCAPE '!'

2. **Associative array method:**

         $array = array('title' => $match, 'page1' => $match, 'page2' => $match);
         $this->db->like($array);
         // WHERE `title` LIKE '%match%' ESCAPE '!' AND  `page1` LIKE '%match%' ESCAPE '!' AND  `page2` LIKE '%match%' ESCAPE '!'

**$this->db->or_like()**

This method is identical to the one above, except that multiple
instances are joined by OR:

   $this->db->like('title', 'match'); $this->db->or_like('body', $match);
   // WHERE `title` LIKE '%match%' ESCAPE '!' OR  `body` LIKE '%match%' ESCAPE '!'

Note:

  "or_like()" was formerly known as "orlike()", which has been
  removed.

**$this->db->not_like()**

This method is identical to "like()", except that it generates NOT
LIKE statements:

   $this->db->not_like('title', 'match');  // WHERE `title` NOT LIKE '%match% ESCAPE '!'

**$this->db->or_not_like()**

This method is identical to "not_like()", except that multiple
instances are joined by OR:

   $this->db->like('title', 'match');
   $this->db->or_not_like('body', 'match');
   // WHERE `title` LIKE '%match% OR  `body` NOT LIKE '%match%' ESCAPE '!'

**$this->db->group_by()**

Permits you to write the GROUP BY portion of your query:

   $this->db->group_by("title"); // Produces: GROUP BY title

You can also pass an array of multiple values as well:

   $this->db->group_by(array("title", "date"));  // Produces: GROUP BY title, date

Note:

  group_by() was formerly known as groupby(), which has been removed.

**$this->db->distinct()**

Adds the “DISTINCT” keyword to a query

   $this->db->distinct();
   $this->db->get('table'); // Produces: SELECT DISTINCT * FROM table

**$this->db->having()**

Permits you to write the HAVING portion of your query. There are 2
possible syntaxes, 1 argument or 2:

   $this->db->having('user_id = 45');  // Produces: HAVING user_id = 45
   $this->db->having('user_id',  45);  // Produces: HAVING user_id = 45

You can also pass an array of multiple values as well:

   $this->db->having(array('title =' => 'My Title', 'id <' => $id));
   // Produces: HAVING title = 'My Title', id < 45

If you are using a database that CodeIgniter escapes queries for, you
can prevent escaping content by passing an optional third argument,
and setting it to FALSE.

   $this->db->having('user_id',  45);  // Produces: HAVING `user_id` = 45 in some databases such as MySQL
   $this->db->having('user_id',  45, FALSE);  // Produces: HAVING user_id = 45

**$this->db->or_having()**

Identical to having(), only separates multiple clauses with “OR”.


Ordering results
================

**$this->db->order_by()**

Lets you set an ORDER BY clause.

The first parameter contains the name of the column you would like to
order by.

The second parameter lets you set the direction of the result. Options
are **ASC**, **DESC** AND **RANDOM**.

   $this->db->order_by('title', 'DESC');
   // Produces: ORDER BY `title` DESC

You can also pass your own string in the first parameter:

   $this->db->order_by('title DESC, name ASC');
   // Produces: ORDER BY `title` DESC, `name` ASC

Or multiple function calls can be made if you need multiple fields.

   $this->db->order_by('title', 'DESC');
   $this->db->order_by('name', 'ASC');
   // Produces: ORDER BY `title` DESC, `name` ASC

If you choose the **RANDOM** direction option, then the first
parameters will be ignored, unless you specify a numeric seed value.

   $this->db->order_by('title', 'RANDOM');
   // Produces: ORDER BY RAND()

   $this->db->order_by(42, 'RANDOM');
   // Produces: ORDER BY RAND(42)

Note:

  order_by() was formerly known as orderby(), which has been removed.

Note:

  Random ordering is not currently supported in Oracle and will
  default to ASC instead.


Limiting or Counting Results
============================

**$this->db->limit()**

Lets you limit the number of rows you would like returned by the
query:

   $this->db->limit(10);  // Produces: LIMIT 10

The second parameter lets you set a result offset.

   $this->db->limit(10, 20);  // Produces: LIMIT 20, 10 (in MySQL.  Other databases have slightly different syntax)

**$this->db->count_all_results()**

Permits you to determine the number of rows in a particular Active
Record query. Queries will accept Query Builder restrictors such as
"where()", "or_where()", "like()", "or_like()", etc. Example:

   echo $this->db->count_all_results('my_table');  // Produces an integer, like 25
   $this->db->like('title', 'match');
   $this->db->from('my_table');
   echo $this->db->count_all_results(); // Produces an integer, like 17

However, this method also resets any field values that you may have
passed to "select()". If you need to keep them, you can pass "FALSE"
as the second parameter:

   echo $this->db->count_all_results('my_table', FALSE);

**$this->db->count_all()**

Permits you to determine the number of rows in a particular table.
Submit the table name in the first parameter. Example:

   echo $this->db->count_all('my_table');  // Produces an integer, like 25


Query grouping
==============

Query grouping allows you to create groups of WHERE clauses by
enclosing them in parentheses. This will allow you to create queries
with complex WHERE clauses. Nested groups are supported. Example:

   $this->db->select('*')->from('my_table')
           ->group_start()
                   ->where('a', 'a')
                   ->or_group_start()
                           ->where('b', 'b')
                           ->where('c', 'c')
                   ->group_end()
           ->group_end()
           ->where('d', 'd')
   ->get();

   // Generates:
   // SELECT * FROM (`my_table`) WHERE ( `a` = 'a' OR ( `b` = 'b' AND `c` = 'c' ) ) AND `d` = 'd'

Note:

  groups need to be balanced, make sure every group_start() is matched
  by a group_end().

**$this->db->group_start()**

Starts a new group by adding an opening parenthesis to the WHERE
clause of the query.

**$this->db->or_group_start()**

Starts a new group by adding an opening parenthesis to the WHERE
clause of the query, prefixing it with ‘OR’.

**$this->db->not_group_start()**

Starts a new group by adding an opening parenthesis to the WHERE
clause of the query, prefixing it with ‘NOT’.

**$this->db->or_not_group_start()**

Starts a new group by adding an opening parenthesis to the WHERE
clause of the query, prefixing it with ‘OR NOT’.

**$this->db->group_end()**

Ends the current group by adding an closing parenthesis to the WHERE
clause of the query.


Inserting Data
==============

**$this->db->insert()**

Generates an insert string based on the data you supply, and runs the
query. You can either pass an **array** or an **object** to the
function. Here is an example using an array:

   $data = array(
           'title' => 'My title',
           'name' => 'My Name',
           'date' => 'My date'
   );

   $this->db->insert('mytable', $data);
   // Produces: INSERT INTO mytable (title, name, date) VALUES ('My title', 'My name', 'My date')

The first parameter will contain the table name, the second is an
associative array of values.

Here is an example using an object:

   /*
   class Myclass {
           public $title = 'My Title';
           public $content = 'My Content';
           public $date = 'My Date';
   }
   */

   $object = new Myclass;
   $this->db->insert('mytable', $object);
   // Produces: INSERT INTO mytable (title, content, date) VALUES ('My Title', 'My Content', 'My Date')

The first parameter will contain the table name, the second is an
object.

Note:

  All values are escaped automatically producing safer queries.

**$this->db->get_compiled_insert()**

Compiles the insertion query just like $this->db->insert() but does
not *run* the query. This method simply returns the SQL query as a
string.

Example:

   $data = array(
           'title' => 'My title',
           'name'  => 'My Name',
           'date'  => 'My date'
   );

   $sql = $this->db->set($data)->get_compiled_insert('mytable');
   echo $sql;

   // Produces string: INSERT INTO mytable (`title`, `name`, `date`) VALUES ('My title', 'My name', 'My date')

The second parameter enables you to set whether or not the query
builder query will be reset (by default it will be–just like
$this->db->insert()):

   echo $this->db->set('title', 'My Title')->get_compiled_insert('mytable', FALSE);

   // Produces string: INSERT INTO mytable (`title`) VALUES ('My Title')

   echo $this->db->set('content', 'My Content')->get_compiled_insert();

   // Produces string: INSERT INTO mytable (`title`, `content`) VALUES ('My Title', 'My Content')

The key thing to notice in the above example is that the second query
did not utilize *$this->db->from()* nor did it pass a table name into
the first parameter. The reason this worked is because the query has
not been executed using *$this->db->insert()* which resets values or
reset directly using *$this->db->reset_query()*.

Note:

  This method doesn’t work for batched inserts.

**$this->db->insert_batch()**

Generates an insert string based on the data you supply, and runs the
query. You can either pass an **array** or an **object** to the
function. Here is an example using an array:

   $data = array(
           array(
                   'title' => 'My title',
                   'name' => 'My Name',
                   'date' => 'My date'
           ),
           array(
                   'title' => 'Another title',
                   'name' => 'Another Name',
                   'date' => 'Another date'
           )
   );

   $this->db->insert_batch('mytable', $data);
   // Produces: INSERT INTO mytable (title, name, date) VALUES ('My title', 'My name', 'My date'),  ('Another title', 'Another name', 'Another date')

The first parameter will contain the table name, the second is an
associative array of values.

Note:

  All values are escaped automatically producing safer queries.


Updating Data
=============

**$this->db->replace()**

This method executes a REPLACE statement, which is basically the SQL
standard for (optional) DELETE + INSERT, using *PRIMARY* and *UNIQUE*
keys as the determining factor. In our case, it will save you from the
need to implement complex logics with different combinations of
"select()", "update()", "delete()" and "insert()" calls.

Example:

   $data = array(
           'title' => 'My title',
           'name'  => 'My Name',
           'date'  => 'My date'
   );

   $this->db->replace('table', $data);

   // Executes: REPLACE INTO mytable (title, name, date) VALUES ('My title', 'My name', 'My date')

In the above example, if we assume that the *title* field is our
primary key, then if a row containing ‘My title’ as the *title* value,
that row will be deleted with our new row data replacing it.

Usage of the "set()" method is also allowed and all fields are
automatically escaped, just like with "insert()".

**$this->db->set()**

This function enables you to set values for inserts or updates.

**It can be used instead of passing a data array directly to the
insert or update functions:**

   $this->db->set('name', $name);
   $this->db->insert('mytable');  // Produces: INSERT INTO mytable (`name`) VALUES ('{$name}')

If you use multiple function called they will be assembled properly
based on whether you are doing an insert or an update:

   $this->db->set('name', $name);
   $this->db->set('title', $title);
   $this->db->set('status', $status);
   $this->db->insert('mytable');

**set()** will also accept an optional third parameter ("$escape"),
that will prevent data from being escaped if set to FALSE. To
illustrate the difference, here is "set()" used both with and without
the escape parameter.

   $this->db->set('field', 'field+1', FALSE);
   $this->db->where('id', 2);
   $this->db->update('mytable'); // gives UPDATE mytable SET field = field+1 WHERE id = 2

   $this->db->set('field', 'field+1');
   $this->db->where('id', 2);
   $this->db->update('mytable'); // gives UPDATE `mytable` SET `field` = 'field+1' WHERE `id` = 2

You can also pass an associative array to this function:

   $array = array(
           'name' => $name,
           'title' => $title,
           'status' => $status
   );

   $this->db->set($array);
   $this->db->insert('mytable');

Or an object:

   /*
   class Myclass {
           public $title = 'My Title';
           public $content = 'My Content';
           public $date = 'My Date';
   }
   */

   $object = new Myclass;
   $this->db->set($object);
   $this->db->insert('mytable');

**$this->db->update()**

Generates an update string and runs the query based on the data you
supply. You can pass an **array** or an **object** to the function.
Here is an example using an array:

   $data = array(
           'title' => $title,
           'name' => $name,
           'date' => $date
   );

   $this->db->where('id', $id);
   $this->db->update('mytable', $data);
   // Produces:
   //
   //      UPDATE mytable
   //      SET title = '{$title}', name = '{$name}', date = '{$date}'
   //      WHERE id = $id

Or you can supply an object:

   /*
   class Myclass {
           public $title = 'My Title';
           public $content = 'My Content';
           public $date = 'My Date';
   }
   */

   $object = new Myclass;
   $this->db->where('id', $id);
   $this->db->update('mytable', $object);
   // Produces:
   //
   // UPDATE `mytable`
   // SET `title` = '{$title}', `name` = '{$name}', `date` = '{$date}'
   // WHERE id = `$id`

Note:

  All values are escaped automatically producing safer queries.

You’ll notice the use of the $this->db->where() function, enabling you
to set the WHERE clause. You can optionally pass this information
directly into the update function as a string:

   $this->db->update('mytable', $data, "id = 4");

Or as an array:

   $this->db->update('mytable', $data, array('id' => $id));

You may also use the $this->db->set() function described above when
performing updates.

**$this->db->update_batch()**

Generates an update string based on the data you supply, and runs the
query. You can either pass an **array** or an **object** to the
function. Here is an example using an array:

   $data = array(
      array(
         'title' => 'My title' ,
         'name' => 'My Name 2' ,
         'date' => 'My date 2'
      ),
      array(
         'title' => 'Another title' ,
         'name' => 'Another Name 2' ,
         'date' => 'Another date 2'
      )
   );

   $this->db->update_batch('mytable', $data, 'title');

   // Produces:
   // UPDATE `mytable` SET `name` = CASE
   // WHEN `title` = 'My title' THEN 'My Name 2'
   // WHEN `title` = 'Another title' THEN 'Another Name 2'
   // ELSE `name` END,
   // `date` = CASE
   // WHEN `title` = 'My title' THEN 'My date 2'
   // WHEN `title` = 'Another title' THEN 'Another date 2'
   // ELSE `date` END
   // WHERE `title` IN ('My title','Another title')

The first parameter will contain the table name, the second is an
associative array of values, the third parameter is the where key.

Note:

  All values are escaped automatically producing safer queries.

Note:

  "affected_rows()" won’t give you proper results with this method,
  due to the very nature of how it works. Instead, "update_batch()"
  returns the number of rows affected.

**$this->db->get_compiled_update()**

This works exactly the same way as "$this->db->get_compiled_insert()"
except that it produces an UPDATE SQL string instead of an INSERT SQL
string.

For more information view documentation for
*$this->db->get_compiled_insert()*.

Note:

  This method doesn’t work for batched updates.


Deleting Data
=============

**$this->db->delete()**

Generates a delete SQL string and runs the query.

   $this->db->delete('mytable', array('id' => $id));  // Produces: // DELETE FROM mytable  // WHERE id = $id

The first parameter is the table name, the second is the where clause.
You can also use the where() or or_where() functions instead of
passing the data to the second parameter of the function:

   $this->db->where('id', $id);
   $this->db->delete('mytable');

   // Produces:
   // DELETE FROM mytable
   // WHERE id = $id

An array of table names can be passed into delete() if you would like
to delete data from more than 1 table.

   $tables = array('table1', 'table2', 'table3');
   $this->db->where('id', '5');
   $this->db->delete($tables);

If you want to delete all data from a table, you can use the
truncate() function, or empty_table().

**$this->db->empty_table()**

Generates a delete SQL string and runs the query.:

   $this->db->empty_table('mytable'); // Produces: DELETE FROM mytable

**$this->db->truncate()**

Generates a truncate SQL string and runs the query.

   $this->db->from('mytable');
   $this->db->truncate();

   // or

   $this->db->truncate('mytable');

   // Produce:
   // TRUNCATE mytable

Note:

  If the TRUNCATE command isn’t available, truncate() will execute as
  “DELETE FROM table”.

**$this->db->get_compiled_delete()**

This works exactly the same way as "$this->db->get_compiled_insert()"
except that it produces a DELETE SQL string instead of an INSERT SQL
string.

For more information view documentation for
$this->db->get_compiled_insert().


Method Chaining
===============

Method chaining allows you to simplify your syntax by connecting
multiple functions. Consider this example:

   $query = $this->db->select('title')
                   ->where('id', $id)
                   ->limit(10, 20)
                   ->get('mytable');


Query Builder Caching
=====================

While not “true” caching, Query Builder enables you to save (or
“cache”) certain parts of your queries for reuse at a later point in
your script’s execution. Normally, when an Query Builder call is
completed, all stored information is reset for the next call. With
caching, you can prevent this reset, and reuse information easily.

Cached calls are cumulative. If you make 2 cached select() calls, and
then 2 uncached select() calls, this will result in 4 select() calls.
There are three Caching functions available:

**$this->db->start_cache()**

This function must be called to begin caching. All Query Builder
queries of the correct type (see below for supported queries) are
stored for later use.

**$this->db->stop_cache()**

This function can be called to stop caching.

**$this->db->flush_cache()**

This function deletes all items from the Query Builder cache.


An example of caching
---------------------

Here’s a usage example:

   $this->db->start_cache();
   $this->db->select('field1');
   $this->db->stop_cache();
   $this->db->get('tablename');
   //Generates: SELECT `field1` FROM (`tablename`)

   $this->db->select('field2');
   $this->db->get('tablename');
   //Generates:  SELECT `field1`, `field2` FROM (`tablename`)

   $this->db->flush_cache();
   $this->db->select('field2');
   $this->db->get('tablename');
   //Generates:  SELECT `field2` FROM (`tablename`)

Note:

  The following statements can be cached: select, from, join, where,
  like, group_by, having, order_by


Resetting Query Builder
=======================

**$this->db->reset_query()**

Resetting Query Builder allows you to start fresh with your query
without executing it first using a method like $this->db->get() or
$this->db->insert(). Just like the methods that execute a query, this
will *not* reset items you’ve cached using Query Builder Caching.

This is useful in situations where you are using Query Builder to
generate SQL (ex. "$this->db->get_compiled_select()") but then choose
to, for instance, run the query:

   // Note that the second parameter of the get_compiled_select method is FALSE
   $sql = $this->db->select(array('field1','field2'))
                                   ->where('field3',5)
                                   ->get_compiled_select('mytable', FALSE);

   // ...
   // Do something crazy with the SQL code... like add it to a cron script for
   // later execution or something...
   // ...

   $data = $this->db->get()->result_array();

   // Would execute and return an array of results of the following query:
   // SELECT field1, field1 from mytable where field3 = 5;

Note:

  Double calls to "get_compiled_select()" while you’re using the Query
  Builder Caching functionality and NOT resetting your queries will
  results in the cache being merged twice. That in turn will i.e. if
  you’re caching a "select()" - select the same field twice.


Class Reference
===============

class CI_DB_query_builder

   reset_query()

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Resets the current Query Builder state.  Useful when you want to
      build a query that can be cancelled under certain conditions.

   start_cache()

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Starts the Query Builder cache.

   stop_cache()

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Stops the Query Builder cache.

   flush_cache()

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Empties the Query Builder cache.

   set_dbprefix([$prefix = ''])

      Parameters:
         * **$prefix** ("string") – The new prefix to use

      Returns:
         The DB prefix in use

      Return type:
         "string"

      Sets the database prefix, without having to reconnect.

   dbprefix([$table = ''])

      Parameters:
         * **$table** ("string") – The table name to prefix

      Returns:
         The prefixed table name

      Return type:
         "string"

      Prepends a database prefix, if one exists in configuration.

   count_all_results([$table = ''[, $reset = TRUE]])

      Parameters:
         * **$table** ("string") – Table name

         * **$reset** ("bool") – Whether to reset values for SELECTs

      Returns:
         Number of rows in the query result

      Return type:
         "int"

      Generates a platform-specific query string that counts all
      records returned by an Query Builder query.

   get([$table = ''[, $limit = NULL[, $offset = NULL]]])

      Parameters:
         * **$table** ("string") – The table to query

         * **$limit** ("int") – The LIMIT clause

         * **$offset** ("int") – The OFFSET clause

      Returns:
         CI_DB_result instance (method chaining)

      Return type:
         "CI_DB_result"

      Compiles and runs SELECT statement based on the already called
      Query Builder methods.

   get_where([$table = ''[, $where = NULL[, $limit = NULL[, $offset = NULL]]]])

      Parameters:
         * **$table** ("mixed") – The table(s) to fetch data from;
           string or array

         * **$where** ("string") – The WHERE clause

         * **$limit** ("int") – The LIMIT clause

         * **$offset** ("int") – The OFFSET clause

      Returns:
         CI_DB_result instance (method chaining)

      Return type:
         "CI_DB_result"

      Same as "get()", but also allows the WHERE to be added directly.

   select([$select = '*'[, $escape = NULL]])

      Parameters:
         * **$select** ("string") – The SELECT portion of a query

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a SELECT clause to a query.

   select_avg([$select = ''[, $alias = '']])

      Parameters:
         * **$select** ("string") – Field to compute the average of

         * **$alias** ("string") – Alias for the resulting value name

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a SELECT AVG(field) clause to a query.

   select_max([$select = ''[, $alias = '']])

      Parameters:
         * **$select** ("string") – Field to compute the maximum of

         * **$alias** ("string") – Alias for the resulting value name

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a SELECT MAX(field) clause to a query.

   select_min([$select = ''[, $alias = '']])

      Parameters:
         * **$select** ("string") – Field to compute the minimum of

         * **$alias** ("string") – Alias for the resulting value name

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a SELECT MIN(field) clause to a query.

   select_sum([$select = ''[, $alias = '']])

      Parameters:
         * **$select** ("string") – Field to compute the sum of

         * **$alias** ("string") – Alias for the resulting value name

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a SELECT SUM(field) clause to a query.

   distinct([$val = TRUE])

      Parameters:
         * **$val** ("bool") – Desired value of the “distinct” flag

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Sets a flag which tells the query builder to add a DISTINCT
      clause to the SELECT portion of the query.

   from($from)

      Parameters:
         * **$from** ("mixed") – Table name(s); string or array

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Specifies the FROM clause of a query.

   join($table, $cond[, $type = ''[, $escape = NULL]])

      Parameters:
         * **$table** ("string") – Table name to join

         * **$cond** ("string") – The JOIN ON condition

         * **$type** ("string") – The JOIN type

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a JOIN clause to a query.

   where($key[, $value = NULL[, $escape = NULL]])

      Parameters:
         * **$key** ("mixed") – Name of field to compare, or
           associative array

         * **$value** ("mixed") – If a single key, compared to this
           value

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         DB_query_builder instance

      Return type:
         "object"

      Generates the WHERE portion of the query. Separates multiple
      calls with ‘AND’.

   or_where($key[, $value = NULL[, $escape = NULL]])

      Parameters:
         * **$key** ("mixed") – Name of field to compare, or
           associative array

         * **$value** ("mixed") – If a single key, compared to this
           value

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         DB_query_builder instance

      Return type:
         "object"

      Generates the WHERE portion of the query. Separates multiple
      calls with ‘OR’.

   or_where_in([$key = NULL[, $values = NULL[, $escape = NULL]]])

      Parameters:
         * **$key** ("string") – The field to search

         * **$values** ("array") – The values searched on

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         DB_query_builder instance

      Return type:
         "object"

      Generates a WHERE field IN(‘item’, ‘item’) SQL query, joined
      with ‘OR’ if appropriate.

   or_where_not_in([$key = NULL[, $values = NULL[, $escape = NULL]]])

      Parameters:
         * **$key** ("string") – The field to search

         * **$values** ("array") – The values searched on

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         DB_query_builder instance

      Return type:
         "object"

      Generates a WHERE field NOT IN(‘item’, ‘item’) SQL query, joined
      with ‘OR’ if appropriate.

   where_in([$key = NULL[, $values = NULL[, $escape = NULL]]])

      Parameters:
         * **$key** ("string") – Name of field to examine

         * **$values** ("array") – Array of target values

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         DB_query_builder instance

      Return type:
         "object"

      Generates a WHERE field IN(‘item’, ‘item’) SQL query, joined
      with ‘AND’ if appropriate.

   where_not_in([$key = NULL[, $values = NULL[, $escape = NULL]]])

      Parameters:
         * **$key** ("string") – Name of field to examine

         * **$values** ("array") – Array of target values

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         DB_query_builder instance

      Return type:
         "object"

      Generates a WHERE field NOT IN(‘item’, ‘item’) SQL query, joined
      with ‘AND’ if appropriate.

   group_start()

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Starts a group expression, using ANDs for the conditions inside
      it.

   or_group_start()

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Starts a group expression, using ORs for the conditions inside
      it.

   not_group_start()

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Starts a group expression, using AND NOTs for the conditions
      inside it.

   or_not_group_start()

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Starts a group expression, using OR NOTs for the conditions
      inside it.

   group_end()

      Returns:
         DB_query_builder instance

      Return type:
         "object"

      Ends a group expression.

   like($field[, $match = ''[, $side = 'both'[, $escape = NULL]]])

      Parameters:
         * **$field** ("string") – Field name

         * **$match** ("string") – Text portion to match

         * **$side** ("string") – Which side of the expression to put
           the ‘%’ wildcard on

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a LIKE clause to a query, separating multiple calls with
      AND.

   or_like($field[, $match = ''[, $side = 'both'[, $escape = NULL]]])

      Parameters:
         * **$field** ("string") – Field name

         * **$match** ("string") – Text portion to match

         * **$side** ("string") – Which side of the expression to put
           the ‘%’ wildcard on

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a LIKE clause to a query, separating multiple class with
      OR.

   not_like($field[, $match = ''[, $side = 'both'[, $escape = NULL]]])

      Parameters:
         * **$field** ("string") – Field name

         * **$match** ("string") – Text portion to match

         * **$side** ("string") – Which side of the expression to put
           the ‘%’ wildcard on

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a NOT LIKE clause to a query, separating multiple calls
      with AND.

   or_not_like($field[, $match = ''[, $side = 'both'[, $escape = NULL]]])

      Parameters:
         * **$field** ("string") – Field name

         * **$match** ("string") – Text portion to match

         * **$side** ("string") – Which side of the expression to put
           the ‘%’ wildcard on

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a NOT LIKE clause to a query, separating multiple calls
      with OR.

   having($key[, $value = NULL[, $escape = NULL]])

      Parameters:
         * **$key** ("mixed") – Identifier (string) or associative
           array of field/value pairs

         * **$value** ("string") – Value sought if $key is an
           identifier

         * **$escape** ("string") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a HAVING clause to a query, separating multiple calls with
      AND.

   or_having($key[, $value = NULL[, $escape = NULL]])

      Parameters:
         * **$key** ("mixed") – Identifier (string) or associative
           array of field/value pairs

         * **$value** ("string") – Value sought if $key is an
           identifier

         * **$escape** ("string") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a HAVING clause to a query, separating multiple calls with
      OR.

   group_by($by[, $escape = NULL])

      Parameters:
         * **$by** ("mixed") – Field(s) to group by; string or array

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds a GROUP BY clause to a query.

   order_by($orderby[, $direction = ''[, $escape = NULL]])

      Parameters:
         * **$orderby** ("string") – Field to order by

         * **$direction** ("string") – The order requested - ASC, DESC
           or random

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds an ORDER BY clause to a query.

   limit($value[, $offset = 0])

      Parameters:
         * **$value** ("int") – Number of rows to limit the results to

         * **$offset** ("int") – Number of rows to skip

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds LIMIT and OFFSET clauses to a query.

   offset($offset)

      Parameters:
         * **$offset** ("int") – Number of rows to skip

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds an OFFSET clause to a query.

   set($key[, $value = ''[, $escape = NULL]])

      Parameters:
         * **$key** ("mixed") – Field name, or an array of field/value
           pairs

         * **$value** ("string") – Field value, if $key is a single
           field

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds field/value pairs to be passed later to "insert()",
      "update()" or "replace()".

   insert([$table = ''[, $set = NULL[, $escape = NULL]]])

      Parameters:
         * **$table** ("string") – Table name

         * **$set** ("array") – An associative array of field/value
           pairs

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         TRUE on success, FALSE on failure

      Return type:
         "bool"

      Compiles and executes an INSERT statement.

   insert_batch($table[, $set = NULL[, $escape = NULL[, $batch_size = 100]]])

      Parameters:
         * **$table** ("string") – Table name

         * **$set** ("array") – Data to insert

         * **$escape** ("bool") – Whether to escape values and
           identifiers

         * **$batch_size** ("int") – Count of rows to insert at once

      Returns:
         Number of rows inserted or FALSE on failure

      Return type:
         "mixed"

      Compiles and executes batch "INSERT" statements.

      Note:

        When more than "$batch_size" rows are provided, multiple
        "INSERT" queries will be executed, each trying to insert up to
        "$batch_size" rows.

   set_insert_batch($key[, $value = ''[, $escape = NULL]])

      Parameters:
         * **$key** ("mixed") – Field name or an array of field/value
           pairs

         * **$value** ("string") – Field value, if $key is a single
           field

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds field/value pairs to be inserted in a table later via
      "insert_batch()".

   update([$table = ''[, $set = NULL[, $where = NULL[, $limit = NULL]]]])

      Parameters:
         * **$table** ("string") – Table name

         * **$set** ("array") – An associative array of field/value
           pairs

         * **$where** ("string") – The WHERE clause

         * **$limit** ("int") – The LIMIT clause

      Returns:
         TRUE on success, FALSE on failure

      Return type:
         "bool"

      Compiles and executes an UPDATE statement.

   update_batch($table[, $set = NULL[, $value = NULL[, $batch_size = 100]]])

      Parameters:
         * **$table** ("string") – Table name

         * **$set** ("array") – Field name, or an associative array of
           field/value pairs

         * **$value** ("string") – Field value, if $set is a single
           field

         * **$batch_size** ("int") – Count of conditions to group in a
           single query

      Returns:
         Number of rows updated or FALSE on failure

      Return type:
         "mixed"

      Compiles and executes batch "UPDATE" statements.

      Note:

        When more than "$batch_size" field/value pairs are provided,
        multiple queries will be executed, each handling up to
        "$batch_size" field/value pairs.

   set_update_batch($key[, $value = ''[, $escape = NULL]])

      Parameters:
         * **$key** ("mixed") – Field name or an array of field/value
           pairs

         * **$value** ("string") – Field value, if $key is a single
           field

         * **$escape** ("bool") – Whether to escape values and
           identifiers

      Returns:
         CI_DB_query_builder instance (method chaining)

      Return type:
         "CI_DB_query_builder"

      Adds field/value pairs to be updated in a table later via
      "update_batch()".

   replace([$table = ''[, $set = NULL]])

      Parameters:
         * **$table** ("string") – Table name

         * **$set** ("array") – An associative array of field/value
           pairs

      Returns:
         TRUE on success, FALSE on failure

      Return type:
         "bool"

      Compiles and executes a REPLACE statement.

   delete([$table = ''[, $where = ''[, $limit = NULL[, $reset_data = TRUE]]]])

      Parameters:
         * **$table** ("mixed") – The table(s) to delete from; string
           or array

         * **$where** ("string") – The WHERE clause

         * **$limit** ("int") – The LIMIT clause

         * **$reset_data** ("bool") – TRUE to reset the query “write”
           clause

      Returns:
         CI_DB_query_builder instance (method chaining) or FALSE on
         failure

      Return type:
         "mixed"

      Compiles and executes a DELETE query.

   truncate([$table = ''])

      Parameters:
         * **$table** ("string") – Table name

      Returns:
         TRUE on success, FALSE on failure

      Return type:
         "bool"

      Executes a TRUNCATE statement on a table.

      Note:

        If the database platform in use doesn’t support TRUNCATE, a
        DELETE statement will be used instead.

   empty_table([$table = ''])

      Parameters:
         * **$table** ("string") – Table name

      Returns:
         TRUE on success, FALSE on failure

      Return type:
         "bool"

      Deletes all records from a table via a DELETE statement.

   get_compiled_select([$table = ''[, $reset = TRUE]])

      Parameters:
         * **$table** ("string") – Table name

         * **$reset** ("bool") – Whether to reset the current QB
           values or not

      Returns:
         The compiled SQL statement as a string

      Return type:
         "string"

      Compiles a SELECT statement and returns it as a string.

   get_compiled_insert([$table = ''[, $reset = TRUE]])

      Parameters:
         * **$table** ("string") – Table name

         * **$reset** ("bool") – Whether to reset the current QB
           values or not

      Returns:
         The compiled SQL statement as a string

      Return type:
         "string"

      Compiles an INSERT statement and returns it as a string.

   get_compiled_update([$table = ''[, $reset = TRUE]])

      Parameters:
         * **$table** ("string") – Table name

         * **$reset** ("bool") – Whether to reset the current QB
           values or not

      Returns:
         The compiled SQL statement as a string

      Return type:
         "string"

      Compiles an UPDATE statement and returns it as a string.

   get_compiled_delete([$table = ''[, $reset = TRUE]])

      Parameters:
         * **$table** ("string") – Table name

         * **$reset** ("bool") – Whether to reset the current QB
           values or not

      Returns:
         The compiled SQL statement as a string

      Return type:
         "string"

      Compiles a DELETE statement and returns it as a string.
