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.

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Markus Winand is the SQL Renaissance Ambassador. He is on a mission to introduce developers to the evolution of SQL in the 21st century. Markus can be hired as trainer, speaker and consultant via winand.at.

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