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D. Using EXPLAIN

Appendix D. Using EXPLAIN

This appendix shows you how to invoke EXPLAIN to get information about the query execution plan, and how to interpret the output. The EXPLAIN command is the main way to find out how the query optimizer decides to execute queries. This feature has limitations and doesn’t always tell the truth, but its output is the best information available, and it’s worth studying so you can learn how your queries are executed. Learning to interpret EXPLAIN will also help you learn how MySQL’s optimizer works.


  

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