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Date: Mon, 3 Nov 2003 17:35:11 -0800
To: Tom Lane <tgl@sss.pgh.pa.us>
From: "Henry B. Hotz" <hotz@jpl.nasa.gov>
Subject: Re: INNER JOINS in sql-select.html
Cc: Stefan Weiss <spaceman-4b9f8-20030703@ausgehaucht.sensenmann.at>,
	pgsql-docs@postgresql.org
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At 7:38 PM -0500 11/3/03, Tom Lane wrote:
>"Henry B. Hotz" <hotz@jpl.nasa.gov> writes:
>>  You can imply the issue without obfuscating things.  How about:
>
>>  A CROSS JOIN or INNER JOIN is a simple Cartesian product, the same
>>  as you get from listing the two items at the top level of FROM.
>>  CROSS JOIN yields the same results as INNER JOIN ON (TRUE), that is,
>>  no rows are removed by qualification.
>
>Okay, but that doesn't do the trick --- it implies that CROSS JOIN isn't
>equivalent to INNER JOIN ON (TRUE), when in fact they are equivalent,
>both as to result and performance characteristics.  The issue at hand is
>that an explicit "a JOIN b" may not be equivalent to "FROM a, b".
>
>I reworded the passage as
>
>         CROSS JOIN and INNER JOIN
>         produce a simple Cartesian product, the same result as you get from
>         listing the two items at the top level of FROM,
>	but restricted by the join condition (if any).
>         CROSS JOIN is equivalent to INNER JOIN ON
>         (TRUE), that is, no rows are removed by qualification.
>
>does that help?

'sarright.  I was just wordsmithing without worrying about the meaning.
-- 
The opinions expressed in this message are mine,
not those of Caltech, JPL, NASA, or the US Government.
Henry.B.Hotz@jpl.nasa.gov, or hbhotz@oxy.edu