Re: Functional dependencies and GROUP BY

Stephen Frost <sfrost@snowman.net> writes:
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>> Perhaps the correct fix would be to mark stored query trees as having a
>> dependency on the index, so that dropping the index/constraint would
>> force a drop of the rule too.

> Alternatively, we could rewrite the rule (not unlike what we do for
> "SELECT *") to actually add on the other implicitly grouped-by columns..
> I don't know if that's better or worse than creating a dependency,
> since if the constraint were dropped/changed, people might expect the
> rule's output to change.

Hm.  The problem with that is that one of the benefits we'd like to get
from this is an efficiency win: the generated plan ought to only group
by the PK, not uselessly sort/group by everything in the row.  I suppose
we could have the planner reverse-engineer its way to that, but it seems
awfully slow and clunky to add on the extra columns and then reason our
way to removing them again.
        regards, tom lane