Re: Optimization issue of branching UNION ALL - Mailing list pgsql-hackers

I wrote:
> Richard Guo <guofenglinux@gmail.com> writes:
>> I noticed we also check 'parse->hasSubLinks' when we fix PHVs and
>> AppendRelInfos in pull_up_simple_subquery.  I'm not sure why we have
>> this check.  It seems not necessary.

> Yeah, I was wondering about that too ... maybe it was important
> in some previous state of the code?  I didn't do any archeology
> though.

After a bit of "git blame"-ing, it appears that that hasSubLinks
check was introduced in e006a24ad, which added a FlattenedSubLink
node type and needed to fix them up here:

+     * We also have to fix the relid sets of any FlattenedSubLink nodes in
+     * the parent query.  (This could perhaps be done by ResolveNew, but it

Then when I got rid of FlattenedSubLink in e549722a8, I neglected
to remove that check.  So I think maybe we don't need it, but I've
not tested.

            regards, tom lane