MySQL Forums :: Optimizer & Parser :: INNER JOIN (WHERE) vs LEFT JOIN

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Posted by: Veny ()
Date: November 02, 2005 08:12PM


Could anyone point me a reference on information related to JOIN operations?
E.g. if i wrote the following sql:
SELECT * FROM Table1, Table2 WHERE Table1.columnA = Table2.columnB AND Table1.columnA = 5;

Does MySQL filters all record of Table1 with columnA's value equals to 5, and then perform JOIN? Or JOIN is perform first before filtering out the values?
I just would to understand on the performance of the query. Instictively, the first option would be faster.

Secondly, compare the two SQLs:
SELECT * FROM Table1, Table2 WHERE Table1.columnA = Table2.columnB;
SELECT * FROM Table1 LEFT JOIN Table2 ON Table1.columnA = Table2.columnB;

Which would be executed faster? I understand the 2 SQLs have different function. LEFT JOIN should used for scenario if not all record of Table1.columnA exist in Table2.columnB. But assuming it does, which query would be faster?

Thanks much.


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Subject Views Written By Posted
INNER JOIN (WHERE) vs LEFT JOIN 87116 Veny 11/02/2005 08:12PM
Re: INNER JOIN (WHERE) vs LEFT JOIN 24410 Sergey Petrunya 11/03/2005 05:18AM
Re: INNER JOIN (WHERE) vs LEFT JOIN 23977 Sergey Petrunya 11/03/2005 05:26AM

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