Lets’s say you’d like to explain the following SQL.
> User.all
User Load (0.9ms) SELECT `users`.* FROM `users`
=> [#<User: ...snip...
> User.all.to_sql
=> "SELECT `users`.* FROM `users`"
All you need to do is adding .explain to the method.
> User.all.explain
User Load (0.6ms) SELECT `users`.* FROM `users`
=> EXPLAIN for: SELECT `users`.* FROM `users`
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
| 1 | SIMPLE | users | ALL | NULL | NULL | NULL | NULL | xxxx | |
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
1 row in set (0.00 sec)