by Markus Winand.

Getting an Execution Plan


Put explain in front of an SQL statement to retrieve the execution plan.

EXPLAIN SELECT 1

The plan is shown in tabular form (some less important columns removed):

~+-------+------+---------------+------+~+------+------------~
~| table | type | possible_keys | key  |~| rows | Extra
~+-------+------+---------------+------+~+------+------------~
~| NULL  | NULL | NULL          | NULL |~| NULL | No tables...
~+-------+------+---------------+------+~+------+------------~

The most important information is in the TYPE column. Although the MySQL documentation refers to it as “join type”, I prefer to describe it as “access type” because it actually specifies how the data is accessed. The meaning of the type value is described in the next section.

About the Author

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Markus Winand teaches efficient SQL—inhouse and online. He minimizes the development time using modern SQL and optimizes the runtime with smart indexing—for that he also published the book SQL Performance Explained.

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