From: Henry B. Hotz <hotz@jpl.nasa.gov>
To: Tom Lane <tgl@sss.pgh.pa.us>
To: 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 15:08:05 -0800
Message-ID: <p05210602bbcc8fb0d68c@[137.78.212.225]> (raw)
In-Reply-To: <3687.1067554564@sss.pgh.pa.us>
References: <1503129.DJSjvup6Wb@weyoun.foo.at>
<3687.1067554564@sss.pgh.pa.us>
At 5:56 PM -0500 10/30/03, Tom Lane wrote:
>Stefan Weiss <spaceman-4b9f8-20030703@ausgehaucht.sensenmann.at> writes:
>> From <doc/html/sql-select.html>:
> > | 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 is equivalent to INNER JOIN ON (TRUE), that is, no rows are
>> | removed by qualification.
>
>> I thought that by using the second form, you would be able to do
>> 'explicit' joins, effectivly telling the planner in which order to
>> join multiple tables (in case you have to join 10+ tables)?
>
>They are semantically equivalent, but not necessarily the same from a
>performance point of view. The potential performance issues are covered
>elsewhere; I think it would just obfuscate matters to try to include
>that topic here.
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.
--
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: <p05210602bbcc8fb0d68c@[137.78.212.225]>
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