How do I get the execution plan for a view?

I have a schema with a number of views. I need to check the execution plans to make sure the appropriate indexes are in place and being used.

How do I do this?

I'd rather not have to copy and paste the output from show create view into explain, especially as some of the views are built on top of other views and this would be quite a pain.

Use the information_schema.views table

This will generate the EXPLAIN for all views

mysql -uroot -p -AN -e"select concat('explain ',view_definition) from information_schema.views" > /root/ExplainViews.sql

This will generate the EXPLAIN for all views in the mydb database

mysql -uroot -p -AN -e"select concat('explain ',view_definition) from information_schema.views where table_schema = 'mydb'" > /root/ExplainViews.sql

Give it a Try !!!
UPDATE 2012-03-22 11:30 EDT

@MattFenwick, your answer is a whole lot simpler than mine. Here is an example I tried out on my PC running MySQL 5.5.12. I ran EXPLAIN on both the SELECT version from your answer and the EXPLAIN generated from my answer:

mysql> explain select * from bigjoin;
+----+-------------+-------+--------+---------------+---------+---------+---------------+------+-------------+
| id | select_type | table | type   | possible_keys | key     | key_len | ref           | rows | Extra       |
+----+-------------+-------+--------+---------------+---------+---------+---------------+------+-------------+
|  1 | SIMPLE      | k     | index  | NULL          | PRIMARY | 4       | NULL          |   14 | Using index |
|  1 | SIMPLE      | a     | eq_ref | PRIMARY       | PRIMARY | 4       | test.k.id_key |    1 | Using index |
|  1 | SIMPLE      | b     | ALL    | NULL          | NULL    | NULL    | NULL          |    4 |             |
+----+-------------+-------+--------+---------------+---------+---------+---------------+------+-------------+
3 rows in set (0.00 sec)

mysql> explain select `a`.`id_key` AS `id_key1`,`b`.`id_key` AS `id_key2` from ((`test`.`idlist` `k` left join `test`.`id_key_table` `a` on((`k`.`id_key` = `a`.`id_key`))) left join `test`.`new_keys_to_load` `b` on((`k`.`id_key` = `b`.`id_key`)));
+----+-------------+-------+--------+---------------+---------+---------+---------------+------+-------------+
| id | select_type | table | type   | possible_keys | key     | key_len | ref           | rows | Extra       |
+----+-------------+-------+--------+---------------+---------+---------+---------------+------+-------------+
|  1 | SIMPLE      | k     | index  | NULL          | PRIMARY | 4       | NULL          |   14 | Using index |
|  1 | SIMPLE      | a     | eq_ref | PRIMARY       | PRIMARY | 4       | test.k.id_key |    1 | Using index |
|  1 | SIMPLE      | b     | ALL    | NULL          | NULL    | NULL    | NULL          |    4 |             |
+----+-------------+-------+--------+---------------+---------+---------+---------------+------+-------------+
3 rows in set (0.00 sec)

mysql>

They both produced the same EXPLAIN plan. I will change my answer to implement your way. You get a +1 from me although it's +2 for simplicity. You should go ahead and accept your own answer on this one.

Here is an interesting factoid about VIEWs in MySQL : A view is represented in two places in the information_schema database

• information_schema.views : table_schema,table_name identify, and view_definition

• information_schema.tables : table_schema,table_name where ENGINE is NULL

This will generate the EXPLAIN for all views

mysql -uroot -p -AN -e"select concat('explain select * from ',table_schema,'.',table_name,';') from information_schema.tables WHERE engine IS NULL" > /root/ExplainViews.sql

or

mysql -uroot -p -AN -e"select concat('explain select * from ',table_schema,'.',table_name,';') from information_schema.views" > /root/ExplainViews.sql

This will generate the EXPLAIN for all views in the mydb database

mysql -uroot -p -AN -e"select concat('explain select * from ',table_schema,'.',table_name,';') from information_schema.tables WHERE table_schema='mydb' AND engine IS NULL;" > /root/ExplainViews.sql

or

mysql -uroot -p -AN -e"select concat('explain select * from ',table_schema,'.',table_name,';') from information_schema.views WHERE table_schema='mydb';" > /root/ExplainViews.sql

StackExchange Database Administrators Q#15371, answer score: 8