关于mysql优化之IN换INNERJOIN的实例分享

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要将A表查询的ID，匹配B表的ID，并将B表全部内容查询出来：

未优化前：

MySQL [xxuer]> SELECT 
 -> COUNT(*)
 -> FROM
 -> t_cmdb_app_version
 -> WHERE
 -> id IN (SELECT 
 -> pid
 -> FROM
 -> t_cmdb_app_relation UNION SELECT 
 -> rp_id
 -> FROM
 -> t_cmdb_app_relation);
+----------+
| COUNT(*) |
+----------+
| 266 |
+----------+
1 row in set (0.21 sec)

优化后：

MySQL [xxuer]> SELECT 
 -> count(*)
 -> FROM
 -> t_cmdb_app_version a
 -> INNER JOIN
 -> (SELECT 
 -> pid
 -> FROM
 -> t_cmdb_app_relation UNION SELECT 
 -> rp_id
 -> FROM
 -> t_cmdb_app_relation) b ON a.id = b.pid;
+----------+
| count(*) |
+----------+
| 266 |
+----------+
1 row in set (0.00 sec)

查看执行计划对比：

MySQL [xxuer]> explain SELECT 
 -> COUNT(*)
 -> FROM
 -> t_cmdb_app_version
 -> WHERE
 -> id IN (SELECT 
 -> pid
 -> FROM
 -> t_cmdb_app_relation UNION SELECT 
 -> rp_id
 -> FROM
 -> t_cmdb_app_relation);
+----+--------------------+---------------------+-------+---------------+---------+---------+------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+---------------------+-------+---------------+---------+---------+------+------+--------------------------+
| 1 | PRIMARY | t_cmdb_app_version | index | NULL | PRIMARY | 4 | NULL | 659 | Using where; Using index |
| 2 | DEPENDENT SUBQUERY | t_cmdb_app_relation | ALL | NULL | NULL | NULL | NULL | 383 | Using where |
| 3 | DEPENDENT UNION | t_cmdb_app_relation | ALL | NULL | NULL | NULL | NULL | 383 | Using where |
| NULL | UNION RESULT | <union2,3> | ALL | NULL | NULL | NULL | NULL | NULL | Using temporary |
+----+--------------------+---------------------+-------+---------------+---------+---------+------+------+--------------------------+
4 rows in set (0.00 sec)

MySQL [xxuer]> explain SELECT 
 -> count(*)
 -> FROM
 -> t_cmdb_app_version a
 -> INNER JOIN
 -> (SELECT 
 -> pid
 -> FROM
 -> t_cmdb_app_relation UNION SELECT 
 -> rp_id
 -> FROM
 -> t_cmdb_app_relation) b ON a.id = b.pid;
+----+--------------+---------------------+--------+---------------+---------+---------+-------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------+---------------------+--------+---------------+---------+---------+-------+------+--------------------------+
| 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 766 | Using where |
| 1 | PRIMARY | a | eq_ref | PRIMARY | PRIMARY | 4 | b.pid | 1 | Using where; Using index |
| 2 | DERIVED | t_cmdb_app_relation | ALL | NULL | NULL | NULL | NULL | 383 | NULL |
| 3 | UNION | t_cmdb_app_relation | ALL | NULL | NULL | NULL | NULL | 383 | NULL |
| NULL | UNION RESULT | <union2,3> | ALL | NULL | NULL | NULL | NULL | NULL | Using temporary |
+----+--------------+---------------------+--------+---------------+---------+---------+-------+------+--------------------------+
5 rows in set (0.00 sec)