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Re: which is best for JOIN approach
Posted by: Øystein Grøvlen
Date: November 25, 2015 02:14AM

Hi,

I assume that you have indexes on all your id columns.

For the second alternative, the join order is given: a -> b -> ec

For the first alternative, both the join order above and a -> ec -> b is possible.

Whether the processing ec before b is beneficial depends on the size of the tables, and the number of matching ids in the two tables.

In other words, I would choose the first alternative because it gives the Query Optimizer more alternatives to evaluate.

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

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