Getting 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 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 our book “SQL Performance Explained”
Probably the best book on SQL performance I've read
Guillaume Lelarge on Amazon.co.uk (5 stars)

About the Author

Photo of Markus Winand
Markus Winand tunes developers for high SQL performance. He also published the book SQL Performance Explained and offers in-house training as well as remote coaching at http://winand.at/

?Recent questions at
Ask.Use-The-Index-Luke.com

3
votes
2
answers
299
views

pagination with nulls

Oct 22 at 08:28 Markus Winand ♦♦ 771
pagination
2
votes
1
answer
1.9k
views
0
votes
2
answers
1.1k
views

different execution plans after failing over from primary to standby server

Sep 17 at 11:46 Markus Winand ♦♦ 771
oracle index update