From: Henry B. Hotz <hotz@jpl.nasa.gov>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Stefan Weiss <spaceman-4b9f8-20030703@ausgehaucht.sensenmann.at>
Cc: pgsql-docs@postgresql.org
Subject: Re: INNER JOINS in sql-select.html
Date: Mon, 3 Nov 2003 17:35:11 -0800
Message-ID: <p05210608bbccb29c0608@[137.78.212.225]> (raw)
In-Reply-To: <17695.1067906301@sss.pgh.pa.us>
References: <1503129.DJSjvup6Wb@weyoun.foo.at>
<3687.1067554564@sss.pgh.pa.us>
<p05210602bbcc8fb0d68c@[137.78.212.225]>
<17695.1067906301@sss.pgh.pa.us>
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
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To: pgsql-docs@postgresql.org
Cc: hotz@jpl.nasa.gov, tgl@sss.pgh.pa.us, spaceman-4b9f8-20030703@ausgehaucht.sensenmann.at
Subject: Re: INNER JOINS in sql-select.html
In-Reply-To: <p05210608bbccb29c0608@[137.78.212.225]>
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