How do I get the execution plan for a view?

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

This is what I first tried:

mysql> explain view_name;
+---------+------------+------+-----+---------+-------+
| Field   | Type       | Null | Key | Default | Extra |
+---------+------------+------+-----+---------+-------+
| field1  | varchar(3) | YES  |     | NULL    |       |
| field2  | varchar(3) | YES  |     | NULL    |       |
| field3  | bigint(21) | NO   |     | 0       |       |
| field4  | bigint(21) | NO   |     | 0       |       |
+---------+------------+------+-----+---------+-------+

Obviously this doesn't work -- it's the same as doing describe view_name.

However, select * from view_name seems to work:

mysql> explain select * from view_name;
+----+-------------+------------+------+---------------+------+---------+------+------+---------------------------------+
| id | select_type | table      | type | possible_keys | key  | key_len | ref  | rows | Extra                           |
+----+-------------+------------+------+---------------+------+---------+------+------+---------------------------------+
|  1 | PRIMARY     | <derived5> | ALL  | NULL          | NULL | NULL    | NULL |   18 |                                 |
|  1 | PRIMARY     | <derived3> | ALL  | NULL          | NULL | NULL    | NULL |  105 | Using where; Using join buffer  |
|  5 | DERIVED     | <derived6> | ALL  | NULL          | NULL | NULL    | NULL |   68 | Using temporary; Using filesort |
|  6 | DERIVED     | basetable  | ALL  | NULL          | NULL | NULL    | NULL |  928 | Using temporary; Using filesort |
|  3 | DERIVED     | <derived4> | ALL  | NULL          | NULL | NULL    | NULL |  386 | Using temporary; Using filesort |
|  4 | DERIVED     | basetable  | ALL  | NULL          | NULL | NULL    | NULL |  928 | Using temporary; Using filesort |
+----+-------------+------------+------+---------------+------+---------+------+------+---------------------------------+