From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | David Johnston <david(dot)g(dot)johnston(at)gmail(dot)com> |
Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, "pgsql-bugs(at)postgresql(dot)org" <pgsql-bugs(at)postgresql(dot)org> |
Subject: | Re: BUG #12000: "CROSS JOIN" not equivalent to "," |
Date: | 2014-11-18 18:40:03 |
Message-ID: | 17013.1416336003@sss.pgh.pa.us |
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Lists: | pgsql-bugs |
David Johnston <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> On Tuesday, November 18, 2014, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
> wrote:
>> Note that using explicit join form force the optimizer into some
>> specific join order, depending on the join_collapse_limit parameter,
>> whereas using commas gives it absolute freedom regardless of the
>> parameter.
> Only because the parameter used in that case is "from_collapse_limit"...
IIRC, from_collapse_limit only affects the behavior when deciding whether
to collapse a mixture of JOIN and comma syntax; it does not change the
outcome if you write a whole bunch of tables in a comma-separated list to
start with.
In any case, such implementation artifacts shouldn't drive our
consideration of what's the clearest way to document this SQL-standard
behavior.
regards, tom lane
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