2011-07-30Getting a MySQL 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 the expression "access type" because it actually specifies how the data is accessed. The meaning of the type values are described in the next section.