Symfony DQL not executing subquery - php

Question

I'm quite new to DQL and I've got a problem with subqueries.
I need to get a list of videoIDs that got added in query2 after the last execution of an optimization.
Symfony is throwing me this exception:
[Syntax Error] line 0, col -1: Error: Expected Doctrine\ORM\Query\Lexer::T_CLOSE_PARENTHESIS, got end of string.
I think the error is generated by the subquery.
Do you know why? Or do you have another way - maybe simpler - of doing this?
This is my code:
public function showOptimizable(){
$query = $this->em->createQuery('
SELECT e.videoID
FROM AppBundle:Query2 e
WHERE e.timestamp < (
SELECT MAX(o.lastOptimization)
FROM AppBundle:Optimization
)
GROUP BY e.videoID HAVING COUNT(e.videoID) < 3
ORDER BY e.videoID DESC
');
return $query->getResult();
}
This is query2:
CREATE TABLE `query2` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`query` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`timestamp` datetime NOT NULL,
`ip` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`uAgent` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`videoID` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`trackTitle` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`present` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `UNIQ_2D293848A5D6E63E` (`timestamp`)
)
And this is optimization:
CREATE TABLE `optimization` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`lastOptimization` datetime NOT NULL,
`optimizedElements` int(11) NOT NULL,
PRIMARY KEY (`id`)
)

Answer 1

The alias "o" is missing. Try this:
(
SELECT MAX(o.lastOptimization)
FROM AppBundle:Optimization o
)