"Cannot group by undefined identification or result variable." when applying filter

[hvanoch]

When we use a SQLfunction inside the Group By statement in the datagrid we get the error Cannot group by undefined identification or result variablewhen applying a filter on a toManyrelation. This is caused by https://github.com/oroinc/platform/blob/d93ef23734d61d63688b2266dc5e99e96f25c914/src/Oro/Bundle/FilterBundle/Filter/AbstractFilter.php#L121

when using a doctrine function in a group by it should also be put inside the select (as AS HIDDEN)

[anyt]

Internal ticket id BAP-20456.