作者：老葛，北京亚艾元软件有限责任公司，http://www.yaiyuan.com
下面有几个例子，希望能够更好的帮助理解条件语句。为了清晰起见，我们在注释中给出等价的查询字符串，当然在实际的应用中，将会使用占位符和预备语句（prepared statements）。
<?php
db_delete('sessions')
->condition('timestamp', REQUEST_TIME - $lifetime, '<')
->execute();
// DELETE FROM {sessions} WHERE (timestamp < 1228713473)
?>
<?php
db_update('sessions')
->fields(array(
'sid' => session_id()
))
->condition('sid', $old_session_id)
->execute();
// UPDATE {sessions} SET sid = 'abcde' WHERE (sid = 'fghij');
?>
<?php
// From taxonomy_term_save():
$or = db_or()->condition('tid1', 5)->condition('tid2', 6);
db_delete('term_relation')->condition($or)->execute();
// DELETE FROM {term_relation} WHERE ((tid1 = 5 OR tid2 = 6))
?>
