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From: Henry B. Hotz <[email protected]>
To: Tom Lane <[email protected]>
Cc: Stefan Weiss <[email protected]>
Cc: [email protected]
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: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<p05210602bbcc8fb0d68c@[137.78.212.225]>
	<[email protected]>

At 7:38 PM -0500 11/3/03, Tom Lane wrote:
>"Henry B. Hotz" <[email protected]> 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.
[email protected], or [email protected]

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