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

Hi,

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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Subject Views Written By Posted
Left join vs Inner join 737 Vikas Sood 05/09/2016 06:10PM
Re: Left join vs Inner join 381 Øystein Grøvlen 05/10/2016 08:04AM
Re: Left join vs Inner join 341 Vikas Sood 05/10/2016 10:40AM
Re: Left join vs Inner join 338 Rick James 05/10/2016 07:23PM


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