• DEPENDENT UNION和DEPENDENT SUBQUERY：当语句中子查询和union查询依赖外部查询会出现。

mysql root@localhost:employees> explain select * from employees e where e.emp_no in (select d.emp_no from dept_emp d where d.from_date = '1986-06-
                                26' union select d.emp_no from dept_emp d where d.from_date = '1996-08-03');
+--------+--------------------+------------+------------+------+---------------+---------+---------+--------+--------+----------+-----------------+
| id     | select_type        | table      | partitions | type | possible_keys | key     | key_len | ref    | rows   | filtered | Extra          |
+--------+--------------------+------------+------------+------+---------------+---------+---------+--------+--------+----------+-----------------+
| 1      | PRIMARY            | e          | <null>     | ALL  | <null>        | <null>  | <null>  | <null> | 299512 | 100.0    | Using where    |
| 2      | DEPENDENT SUBQUERY | d          | <null>     | ref  | PRIMARY       | PRIMARY | 4       | func   | 1      |  10.0    | Using where    |
| 3      | DEPENDENT UNION    | d          | <null>     | ref  | PRIMARY       | PRIMARY | 4       | func   | 1      |  10.0    | Using where    |
| <null> | UNION RESULT       | <union2,3> | <null>     | ALL  | <null>        | <null>  | <null>  | <null> | <null> | <null>   | Using temporary|
+--------+--------------------+------------+------------+------+---------------+---------+---------+--------+--------+----------+-----------------+
4 rows in set
Time: 0.022s

• DERIVED：当查询涉及生成临时表时出现。

mysql root@localhost:employees> explain select * from (select * from departments limit 5) de;
+----+-------------+-------------+------------+-------+---------------+-----------+---------+--------+------+----------+-------------+
| id | select_type | table       | partitions | type  | possible_keys | key       | key_len | ref    | rows | filtered | Extra       |
+----+-------------+-------------+------------+-------+---------------+-----------+---------+--------+------+----------+-------------+
| 1  | PRIMARY     | <derived2>  | <null>     | ALL   | <null>        | <null>    | <null>  | <null> | 5    | 100.0    | <null>      |
| 2  | DERIVED     | departments | <null>     | index | <null>        | dept_name | 122     | <null> | 9    | 100.0    | Using index |
+----+-------------+-------------+------------+-------+---------------+-----------+---------+--------+------+----------+-------------+
2 rows in set
Time: 0.012s

table

指执行计划当中当前是从哪张表获取数据，如果为表指定了别名，则显示别名，如果没有涉及对表的数据读取，则显示NULL，还有如下几种情形：

1. <unionM,N>：数据来自union查询的id为M和N的结果集；
2. ：数据来自派生表id为N的结果集；
3. ：数据来自子查询id为N的结果集。

partitions

指执行计划中当前从分区表哪个表分区获取数据，如果不是分区表，则显示为NULL。