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Re: INNER JOIN vs WHERE

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "T(dot) Alex Beamish" <talexb(at)tabsoft(dot)on(dot)ca>
Cc: "Postgresql-Performance" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: INNER JOIN vs WHERE
Date: 2003-05-15 02:25:55
Message-ID: 4921.1052965555@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
"T. Alex Beamish" <talexb(at)tabsoft(dot)on(dot)ca> writes:
> Is there any rule of thumb about how much more efficient an INNER JOIN
> is compare to a regular WHERE statement?

Ideally there is no difference.  If there are only two tables involved,
there definitely is no difference.

If there is a difference, it's because there are more than two tables,
and the JOIN syntax forced a particular join order.  Read 
http://www.postgresql.org/docs/view.php?version=7.3&idoc=0&file=explicit-joins.html

Typically I'd expect JOIN syntax to be a loss because the odds are good
that you're forcing an inefficient join order.  It could be a win only
if the planner chooses a poor join order when given a free hand, or if
you have so many tables that you need to suppress the planner's search
for a good join order.

> I have not tried to do an EXPLAIN ANALYZE yet but I will try that.

If you have not bothered to do any EXPLAINs yet then you are really
wasting people's time on this list.

			regards, tom lane

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