From: | Michael Glaesemann <grzm(at)myrealbox(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Steve Tucknott <steve(at)retsol(dot)co(dot)uk>, PostGreSQL <pgsql-novice(at)postgresql(dot)org> |
Subject: | Re: Sequential Scans On Complex Query With UNION - see why this fails |
Date: | 2006-01-12 03:48:27 |
Message-ID: | 08E5AFE4-8B58-4D91-82A1-501419839BE4@myrealbox.com |
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Thread: | |
Lists: | pgsql-novice |
On Jan 12, 2006, at 12:21 , Tom Lane wrote:
> I think what's happening is that the parser implicitly parenthesizes
> like this:
>
> from ((a join b on a.x=b.y) join c on b.y=c.z)
Any idea off hand if the SQL spec has anything to say on the subject?
I haven't dug into my local version of the final draft to see.
>> I believe both join conditions and
>> restrictions are rewritten as they'd appear in the WHERE clause, so
>> you *could* put them all in the WHERE clause.
>
> Again, this is true for inner joins but very much not the case if
> any outer joins are involved.
Thanks for the clarification, Tom. While I was writing I thought that
OUTER JOIN was an exception, but I neglected to look into it or
include my thoughts.
Michael Glaesemann
grzm myrealbox com
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