From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> |
Cc: | luuk(at)wxs(dot)nl, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: [HACKERS] Re: [GENERAL] Re: [PHP3] Re: PostgreSQL vs Mysql comparison |
Date: | 1999-10-05 22:29:45 |
Message-ID: | 12470.939162585@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> writes:
> But can we compare aggs and non-aggs? I see now that our code is fine:
No, you're barking up the wrong tree. The issue is whether a HAVING
clause that doesn't contain *any* aggregates is legal/reasonable.
It can contain non-aggregated references to GROUP BY columns in
any case. But without aggregates, there's no semantic difference
from putting the same condition in WHERE.
I believe that planner.c currently has an implementation assumption
that HAVING must have an aggregate (because it hangs the HAVING clause
onto the Agg plan node as a qual clause --- if no Agg node, no place to
perform the HAVING test). This could be fixed if we felt it was worth
doing.
I can't get excited about changing this from the standpoint of
functionality, because AFAICS there is no added functionality.
But if we're looking bad on a recognized benchmark maybe we
should do something about it.
regards, tom lane
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