select_common_typmod

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select_common_typmod

Peter Eisentraut-6
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.

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()).

--
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

0001-Add-select_common_typmod.patch (10K) Download Attachment
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Re: select_common_typmod

Heikki Linnakangas
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


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Re: select_common_typmod

Peter Eisentraut-6
On 2020-10-26 10:05, Heikki Linnakangas wrote:
>> 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.

Yeah, something like that.

> 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.

OK, committed with that.

--
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services