Re: group by error message?

Louis-David Mitterrand <vindex+lists-pgsql-general(at)apartia(dot)org> writes:
> critik=# select distinct pt.type_fr,sum(e2.id_event) from person_type pt natural join person_to_event join event e using (id_event) LEFT JOIN event e2 ON e.id_event = e2.id_event AND e2.id_event=219 join event_type et ON e.id_event_type = et.id_event_type where et.type_fr='thtre' GROUP BY pt.type_fr IS NULL;

> gives this error:

> ERROR: column "pt.type_fr" must appear in the GROUP BY clause or be used in an aggregate function

> But pt.type_fr is _already_ in the group by.

No, "pt.type_fr IS NULL" is in the group by. That doesn't ensure that
each group has a unique value of pt.type_fr itself.

regards, tom lane