Re: select_common_typmod

On 20/10/2020 11:58, Peter Eisentraut wrote:
> While working on another patch, I figured adding a
> select_common_typmod() to go along with select_common_type() and
> select_common_collation() would be handy.  Typmods were previously
> combined using hand-coded logic in several places, and not at all in
> other places.  The logic in select_common_typmod() isn't very exciting,
> but it makes the code more compact and readable in a few locations, and
> in the future we can perhaps do more complicated things if desired.

Makes sense.

> There might have been a tiny bug in transformValuesClause() because
> while consolidating the typmods it does not take into account whether
> the types are actually the same (as more correctly done in
> transformSetOperationTree() and buildMergedJoinVar()).

Hmm, it seems so, but I could not come up with a test case to reach that 
codepath. I think you'd need to create two types in the same 
typcategory, but with different and incompatible typmod formats.

The patch also adds typmod resolution for hypothetical ordered-set 
aggregate arguments. I couldn't come up with a test case that would 
tickle that codepath either, but it seems like a sensible change. You 
might want to mention it in the commit message though.

- Heikki