From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
Cc: | "Alexey A(dot) Nalbat" <nalbat(at)price(dot)ru>, "Simon Riggs" <simon(at)2ndquadrant(dot)com>, "Decibel!" <decibel(at)decibel(dot)org>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: unnesesary sorting after Merge Full Join |
Date: | 2008-02-26 18:35:34 |
Message-ID: | 5779.1204050934@sss.pgh.pa.us |
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Lists: | pgsql-general |
Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)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
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