mysql 優化例子：IN 換 INNER JOIN
阿新 • • 發佈：2017-06-21
mysql
今天擼代碼時，遇到SQL問題：
要將A表查詢的ID，匹配B表的ID，並將B表全部內容查詢出來：
未優化前：
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)優化後：
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)查看執行計劃對比：
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)本文出自 “隔壁老張” 博客，請務必保留此出處http://xxuer.blog.51cto.com/11947593/1940438
mysql 優化例子：IN 換 INNER JOIN