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Re: Left join vs Inner join
Posted by: Øystein Grøvlen
Date: May 10, 2016 08:04AM


LEFT JOIN requires that left table is processed before right table. Hence, the optimizer has less freedom in which orders tables may be processed.

The major problem with the LEFT JOIN plan is the table scan of the <derived2> table. (Derived tables are subqueries in FROM clause). This is a problem in MySQL 5.5 and earlier because indexed access is not possible for derived tables.

Your best bet is to upgrade to MySQL 5.6.

Øystein Grøvlen,
Senior Principal Software Engineer,
MySQL Group, Oracle,
Trondheim, Norway

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Written By
May 09, 2016 06:10PM
Re: Left join vs Inner join
May 10, 2016 08:04AM
May 10, 2016 10:40AM
May 10, 2016 07:23PM

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