Re: Functional dependencies and GROUP BY

On Tue, Jun 8, 2010 at 4:16 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
>> I have developed a patch that partially implements the "functional
>> dependency" feature that allows some columns to be omitted from the
>> GROUP BY clause if it can be shown that the columns are functionally
>> dependent on the columns in the group by clause and therefore guaranteed
>> to be unique per group.
>
> The main objection to this is the same one I've had all along: it makes
> the syntactic validity of a query dependent on what indexes exist for
> the table.  At minimum, that means that enforcing the check at parse
> time is the Wrong Thing.

It also needs to ensure that the plan is invalidated if the constraint
is dropped, which I assume amounts to the same thing.

--
greg