Symfony doctrine orderby and group by (distinct)

I am trying to get the latest booked courses (unique). I have tried the following with the Doctrine querybuilder:

$repository = $this->getDoctrine()->getRepository('AppBundle:Booking');

$query = $repository->createQueryBuilder('b')
->select('(b.course) AS course')
->orderBy('b.id', 'DESC')
->groupBy('b.course')
->setMaxResults(5)
->getQuery();

Without the orderby it works but it will traverse the bookings ascending. I need the latest booked courses. With this query I am getting this error:

SQLSTATE[42000]: Syntax error or access violation: 1055 Expression #1 of ORDER BY clause is not in GROUP BY clause and contains nonaggregated column … which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by 500 Internal Server Error – DriverException

I also tried the following:

$em = $this->getDoctrine()->getManager();
$query = $em->createQuery(
   'SELECT DISTINCT c.id
    FROM AppBundle:Booking b
    JOIN b.course c
    ORDER BY b.id DESC'
);

SQLSTATE[HY000]: General error: 3065 Expression #1 of ORDER BY clause is not in SELECT list, references column … which is not in SELECT list; this is incompatible with DISTINCT

Now I have searched for solutions and basically found a lot of suggestions to disable ONLY_FULL_GROUP_BY. Disable ONLY_FULL_GROUP_BY

Some comments state there that it is not wise to do that in order to comply to sql standards. Then how is this possible in a way that does work?

Answer

You could try this way:

$query = $repository->createQueryBuilder('b')
->select('(b.course) AS course')
->leftJoin('AppBundle:Booking', 'b2', 'WITH', 'b.course = b2.course AND b.id < b2.id')
->where('b2.id IS NULL')
->orderBy('b.id', 'DESC')
->setMaxResults(5)
->getQuery();

You’ll get only the bookings with greatest id for every course, so no need for grouping by course.

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Answer