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doctrine2/manual/docs/DQL (Doctrine Query Language) - Conditional expressions - Subqueries.php

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2007-04-14 01:49:11 +04:00
A subquery can contain any of the keywords or clauses that an ordinary SELECT query can contain.
Some advantages of the subqueries:
* They allow queries that are structured so that it is possible to isolate each part of a statement.
* They provide alternative ways to perform operations that would otherwise require complex joins and unions.
* They are, in many people's opinion, readable. Indeed, it was the innovation of subqueries that gave people the original idea of calling the early SQL <EFBFBD>Structured Query Language.<EFBFBD>
<code type="php">
// finding all users which don't belong to any group 1
$query = "FROM User WHERE User.id NOT IN
(SELECT u.id FROM User u
INNER JOIN u.Group g WHERE g.id = ?";
$users = $conn->query($query, array(1));
// finding all users which don't belong to any groups
// Notice:
// the usage of INNER JOIN
// the usage of empty brackets preceding the Group component
$query = "FROM User WHERE User.id NOT IN
(SELECT u.id FROM User u
INNER JOIN u.Group g)";
$users = $conn->query($query);
</code>