Re: INNER JOINS in sql-select.html

At 7:38 PM -0500 11/3/03, Tom Lane wrote:
>"Henry B. Hotz" <hotz(at)jpl(dot)nasa(dot)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(dot)B(dot)Hotz(at)jpl(dot)nasa(dot)gov, or hbhotz(at)oxy(dot)edu