Description:
in the example below explain show from which derived tables, the primary select gets its data.
Explain only names this tables as "<derivedN>". since mysql insists on an alias for those tables anyway, it would be nice if this alias could be shown in addition.
How to repeat:
explain select * from (select 1 a) tbl1;
+----+-------------+------------+--------+---------------+------+---------+------+------+----------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra
+----+-------------+------------+--------+---------------+------+---------+------+------+----------------+
| 1 | PRIMARY | <derived2> | system | NULL | NULL | NULL | NULL | 1 |
| 2 | DERIVED | NULL | NULL | NULL | NULL | NULL | NULL | NULL | No tables used |
+----+-------------+------------+--------+---------------+------+---------+------+------+----------------+
2 rows in set (0.00 sec)
# or if any table t1 exists
explain select * from (select * from t1) tbl1;
+----+-------------+------------+------+---------------+------+---------+------+------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+------+---------------+------+---------+------+------+-------+
| 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 22 | |
| 2 | DERIVED | t1 | ALL | NULL | NULL | NULL | NULL | 22 | |
+----+-------------+------------+------+---------------+------+---------+------+------+-------+
Suggested fix:
Modify the result to something like:
explain select * from (select 1 a) tbl1;
+----+-------------+------------+--------+---
| id | select_type | table | type |
+----+-------------+------------+--------+----
| 1 | PRIMARY | tbl1 <derived2> | system |
| 2 | DERIVED | NULL | NULL |
+----+-------------+------------+--------+------
