Re: unnesesary sorting after Merge Full Join

Gregory Stark <stark@enterprisedb.com> writes:
> "Tom Lane" <tgl@sss.pgh.pa.us> writes:
>> It might still be interesting sometime to have a more bespoke
>> representation for a merged variable, but I guess we don't need
>> it just for this.

> It might have an advantage if you're doing a three-way outer join and neither
> C(id1, C(id2,id3)) nor C(C(id2,id3), id1) match the requested order of
> C(C(id1,id2), id3).

Hmm ... couldn't we fix that if the COALESCE-builder were smart enough
to flatten nested COALESCEs?  AFAICS, C(C(x,y),z) == C(x,y,z)

> It doesn't see too important to get that right since the outer joins can't be
> reordered and the user could reasonably be expected to match the grouping of
> his joins with his coalesce expression.

Agreed, it's not real clear that nested full joins are something we need
to be overly tense about right now.

            regards, tom lane