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|
explain
select * from (
select 1 as foo from sakila.actor as actor_1
union
select 1 from sakila.actor as actor_2
) as der_1
union
select * from (
select 1 as foo from sakila.actor as actor_3
union all
select 1 from sakila.actor as actor_4
) as der_2;
+----+--------------+------------+--------+---------------+---------+---------+------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------+------------+--------+---------------+---------+---------+------+------+-------------+
| 1 | PRIMARY | <derived2> | system | NULL | NULL | NULL | NULL | 1 | |
| 2 | DERIVED | actor_1 | index | NULL | PRIMARY | 2 | NULL | 200 | Using index |
| 3 | UNION | actor_2 | index | NULL | PRIMARY | 2 | NULL | 200 | Using index |
| NULL | UNION RESULT | <union2,3> | ALL | NULL | NULL | NULL | NULL | NULL | |
| 4 | UNION | <derived5> | ALL | NULL | NULL | NULL | NULL | 400 | |
| 5 | DERIVED | actor_3 | index | NULL | PRIMARY | 2 | NULL | 200 | Using index |
| 6 | UNION | actor_4 | index | NULL | PRIMARY | 2 | NULL | 200 | Using index |
| NULL | UNION RESULT | <union5,6> | ALL | NULL | NULL | NULL | NULL | NULL | |
| NULL | UNION RESULT | <union1,4> | ALL | NULL | NULL | NULL | NULL | NULL | |
+----+--------------+------------+--------+---------------+---------+---------+------+------+-------------+
|
