mysql - 如何首先且仅运行一次子查询

Question

如何让 MySQL 首先运行子查询并且只运行一次？现在 MySQL 对表 t1 中的每一行运行内部查询，这是一个性能灾难。

explain select * from t1 where uid in (select id from t0);
+----+--------------------+-------+------+---------------+------+---------+------+----------+-------------+
| id | select_type        | table | type | possible_keys | key  | key_len | ref  | rows     | Extra       |
+----+--------------------+-------+------+---------------+------+---------+------+----------+-------------+
|  1 | PRIMARY            | t1    | ALL  | NULL          | NULL | NULL    | NULL | 18954249 | Using where |
|  2 | DEPENDENT SUBQUERY | t0    | ALL  | NULL          | NULL | NULL    | NULL |    12749 | Using where |
+----+--------------------+-------+------+---------------+------+---------+------+----------+-------------+

Answer 1

如果您执行内部联接，您将获得所需的结果。

来自:

select * from t1 where uid in (select id from t0);

收件人:

select * from t1 join t0 on t1.t0id = t0.id

http://en.wikipedia.org/wiki/Join_(SQL)#Inner_join