DQL 中嵌套子查询中的错误:未定义类“("

As you can see, it has three joins. As 'at' and 'ac' both have large amount of data. In attempt to optimize it, I am trying to move the "p.create_analytics = '1'" checking before join to 'ac' to give it a smaller data set to join. I am trying to achieve something like this:

SELECT at, count(at.id) FROM ( SELECT at FROM AccountTriple at JOIN at.property p WHERE p.create_analytics = '1' ) JOIN at.account ac  GROUP BY at.property, at.value, ac.service

但不知何故，我的语法不起作用.错误消息显示如下:

// build root query
$query = Doctrine_Query::create()
  ->from('Movie m')
  ->where('name = ?', 'Prometheus')
;

// build subquery
$subquery = $query->createSubquery()
  ->from('SeenMovie sm')
  ->where('m.name = sm.name')
;

// nest subquery and execute
$query->where('EXISTS (' . $subquery->getDql() . ')')->execute();