Zend_Db_Select is a tool to help you build SQL SELECT statements in a database-independent way. Obviously this can't be perfect, but it does go a long way toward helping your queries be portable between database backends. In addition, it aids you in making your queries resistant to SQL injection attacks.

The easiest way to create an instance of Zend_Db_Select is to use the Zend_Db_Adapter::select() method.

<?php
	
require_once 'Zend/Db.php';

$params = array (
    'host'     => '127.0.0.1',
    'username' => 'malory',
    'password' => '******',
    'dbname'   => 'camelot'
);

$db = Zend_Db::factory('PDO_MYSQL', $params);

$select = $db->select();
// $select is now a Zend_Db_Select object configured for use only with the PDO_MYSQL adapter

?>

You then construct a SELECT query using that object and its methods, then generate a string for passing back to Zend_Db_Adapter for queries or fetches.

<?php
	
//
// SELECT *
//     FROM round_table
//     WHERE noble_title = "Sir"
//     ORDER BY first_name
//     LIMIT 10 OFFSET 20
//

// you can use an iterative style...
$select->from('round_table', '*');
$select->where('noble_title = ?', 'Sir');
$select->order('first_name');
$select->limit(10,20);

// ...or a "fluent" style:
$select->from('round_table', '*')
       ->where('noble_title = ?', 'Sir')
       ->order('first_name')
       ->limit(10,20);

// regardless, fetch the results
$sql = $select->__toString();
$result = $db->fetchAll($sql);

// alternatively, you can pass the $select object itself;
// Zend_Db_Adapter is smart enough to call __toString() on the
// Zend_Db_Select objects to get the query string.
$result = $db->fetchAll($select);

?>

You can also use bound parameters in your queries instead of quoting-as-you-go.

<?php
	
//
// SELECT *
//     FROM round_table
//     WHERE noble_title = "Sir"
//     ORDER BY first_name
//     LIMIT 10 OFFSET 20
//

$select->from('round_table', '*')
       ->where('noble_title = :title')
       ->order('first_name')
       ->limit(10,20);

// regardless, fetch the results using bound parameters
$params = array('title' => 'Sir');
$result = $db->fetchAll($select, $params);

?>

To select columns from a specific table, use the from() method, specifying the table and the columns you want from it. You can use both table and column aliases, and you can use from() as many times as you need.

<?php
	
// create a $db object, assuming Mysql as the adapter.
$select = $db->select();

// SELECT a, b, c FROM some_table
$select->from('some_table', 'a, b, c');
// equivalent:
$select->from('some_table', array('a', 'b', 'c');

// SELECT bar.col FROM foo AS bar
$select->from('foo AS bar', 'bar.col');

// SELECT foo.col AS col1, bar.col AS col2 FROM foo, bar
$select->from('foo', 'foo.col AS col1');
$select->from('bar', 'bar.col AS col2');

?>

To select columns using joined tables, use the join() method. First give the joining table name, then the joining condition, and finally the columns you want from the join. You can use join() as many times as you need.

<?php
	
// create a $db object, assuming Mysql as the adapter.
$select = $db->select();

//
// SELECT foo.*, bar.*
//     FROM foo
//     JOIN bar ON foo.id = bar.id
//
$select->from('foo', '*');
$select->join('bar', 'foo.id = bar.id', '*');

?>

Currently, only the JOIN syntax is supported; no LEFT JOINs, RIGHT JOINs, etc. Future releases will support these in a database-neutral fashion.

To add WHERE conditions, use the where() method. You can pass either a regular string, or you can pass a string with a question-mark placeholder and a value to quote into it (the value will be quoted using Zend_Db_Adapter::quoteInto).

Multiple calls to where() will AND the conditions together; if you need to OR a condition, use orWhere().

<?php
	
// create a $db object, then get a SELECT tool.
$select = $db->select();

//
// SELECT *
//     FROM round_table
//     WHERE noble_title = "Sir"
//     AND favorite_color = "yellow"
//
$select->from('round_table', '*');
$select->where('noble_title = "Sir"'); // embedded value
$select->where('favorite_color = ?', 'yellow'); // quoted value

//
// SELECT *
//     FROM foo
//     WHERE bar = "baz"
//     OR id IN("1", "2", "3")
//
$select->from('foo', '*');
$select->where('bar = ?', 'baz');
$select->orWhere('id IN(?)', array(1, 2, 3);

?>

To group rows, use the group() method as many times as you wish.

<?php
	
// create a $db object, then get a SELECT tool.
$select = $db->select();

//
// SELECT COUNT(id)
//     FROM foo
//     GROUP BY bar, baz
//
$select->from('foo', 'COUNT(id)');
$select->group('bar');
$select->group('baz');

// an equivalent group() call:
$select->group('bar, baz');

// another equivalent group() call:
$select->group(array('bar', 'baz'));

?>

To add HAVING conditions to the selected results, use the having() method. This method is identical in function to the where() method.

If you call having() multiple times, the conditions are ANDed together; if you want to OR a condition, use orHaving().

<?php
	
// create a $db object, then get a SELECT tool.
$select = $db->select();

//
// SELECT COUNT(id) AS count_id
//     FROM foo
//     GROUP BY bar, baz
//     HAVING count_id > "1"
//
$select->from('foo', 'COUNT(id) AS count_id');
$select->group('bar, baz');
$select->having('count_id > ?', 1);

?>

To ORDER columns, use the order() method as many times as you wish.

<?php
	
// create a $db object, then get a SELECT tool.
$select = $db->select();

//
// SELECT * FROM round_table
//     ORDER BY noble_title DESC, first_name ASC
//
$select->from('round_table', '*');
$select->order('noble_title DESC');
$select->order('first_name');

// an equivalent order() call:
$select->order('noble_title DESC, first_name');

// another equivalent order() call:
$select->order(array('noble_title DESC', 'first_name'));

?>

Zend_Db_Select offers database-abstracted LIMIT clause support. For many databases, such as MySQL and PostgreSQL, this is relatively easy, as they support the the "LIMIT :count [OFFSET :offset]" syntax.

For other databases, such as Microsoft SQL and Oracle, this is not so easy, as they do not support LIMIT clauses at all. MS-SQL has only a TOP clause, and Oracle requires that a query be written in a special fashion to emulate a LIMIT. Because of the way Zend_Db_Select works internally, we can rewrite the SELECT on-the-fly to emulate the LIMIT functionality of the aforementioned open-source database systems.

To LIMIT the returned results by count and offset, use the limit() method with a count and optional offset.

<?php
	
// first, a simple "LIMIT :count"
$select = $db->select();
$select->from('foo', '*');
$select->order('id');
$select->limit(10);

//
// In MySQL/PostgreSQL/SQLite, this translates to:
//
// SELECT * FROM foo
//     ORDER BY id ASC
//     LIMIT 10
//
// But in Microsoft SQL, this translates to:
//
// SELECT TOP 10 * FROM FOO
//     ORDER BY id ASC
//
//

// now, a more complex "LIMIT :count OFFSET :offset"
$select = $db->select();
$select->from('foo', '*');
$select->order('id');
$select->limit(10, 20);

//
// In MySQL/PostgreSQL/SQLite, this translates to:
//
// SELECT * FROM foo
//     ORDER BY id ASC
//     LIMIT 10 OFFSET 20
//
// But in Microsoft SQL, which has no offset support, this translates to
// something like:
//
// SELECT * FROM (
//     SELECT TOP 10 * FROM (
//         SELECT TOP 30 * FROM foo ORDER BY id DESC
//     ) ORDER BY id ASC
// )
//
// Zend_Db_Adapter does the query translation for you automatically.
//

?>

Zend_Db_Select offers page-based limits as well. If you wish to retrieve a certain "page" of results, use the limitPage() method; first pass the page number you want, and then the number of rows that appear on each page.

<?php
	
// build the basic select...
$select = $db->select();
$select->from('foo', '*');
$select->order('id');

// ... and limit to page 3 where each page has 10 rows
$select->limitPage(3, 10);

//
// In MySQL/PostgreSQL/SQLite, this translates to:
//
// SELECT * FROM foo
//     ORDER BY id ASC
//     LIMIT 10 OFFSET 20
//

?>