Tests that we can use a subquery in a WHERE clause.
function testConditionSubquerySelect() {
// Create a subquery, which is just a normal query object.
$subquery = db_select('test_task', 'tt');
$subquery
->addField('tt', 'pid', 'pid');
$subquery
->condition('tt.priority', 1);
// Create another query that joins against the virtual table resulting
// from the subquery.
$select = db_select('test_task', 'tt2');
$select
->addField('tt2', 'task');
$select
->condition('tt2.pid', $subquery, 'IN');
// The resulting query should be equivalent to:
// SELECT tt2.name
// FROM test tt2
// WHERE tt2.pid IN (SELECT tt.pid AS pid FROM test_task tt WHERE tt.priority=1)
$people = $select
->execute()
->fetchCol();
$this
->assertEqual(count($people), 5, 'Returned the correct number of rows.');
}