groupBy using alias in Doctrine QueryBuilder
===

Im trying to query a database to get all initials from a table.

In SQL, the query would be:

    SELECT SUBSTRING(t.name, 1, 1) AS initial FROM Tool t GROUP BY initial

But using QueryBuilder, I havn't find the way to group by aliases.

I've tried:

     $q = $this->em->createQueryBuilder()
         ->select('SUBSTRING(i.name, 1, 1) AS initial')
         ->from('...\Entity\Tool', 't')
         ->groupBy('initial');

    Error: 'initial' does not point to a Class.


    $q = $this->em->createQueryBuilder()
         ->select('SUBSTRING(t.name, 1, 1)')
         ->from('...\Entity\Tool', 't')
         ->groupBy('SUBSTRING(t.name, 1, 1)');

    (t.name, 1, ': Error: Cannot group by undefined identification variable.

And after half an hour looking for documentation I'm asking again for help.
Is it possible, or should I go to another way ?

Thanks !