Re: Remove useless GROUP BY columns considering unique index

On Wed, 18 Sept 2024 at 19:28, Peter Eisentraut <peter(at)eisentraut(dot)org> wrote:
>
> On 12.09.24 03:43, David Rowley wrote:
> > (Likely it could just look at pg_attribute.attnotnull instead)
>
> That won't work because you can't record dependencies on that. (This is
> one of the reasons for cataloging not-null constraints as real constraints.)

I'm not seeing any need to record constraint dependencies for this
optimisation. It would be different for detecting functional
dependencies in a view using a unique constraint+not null constraints
for ungrouped columns, but that's not what this is. This is just a
planner optimisation. The plan can be invalidated by a relcache
invalidation, which will happen if someone does ALTER TABLE DROP NOT
NULL.

For reference, see 5b736e9cf.

David