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[PHP] Mysql的一条SQL优化(一)_MySQL-mysql教程

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  • 发表于 2017-5-12 16:11:00 | 显示全部楼层 |阅读模式
    开发反应做压测时并发上不去,有条SQL执行非常慢,于是explain下:
      MariaDB [db_vip]> MariaDB [db_vip]> explain select ext_id, mid, msource_id, msource_type, referee, mobile, tel, mpassword,status from m_db_vip where (msource_id='xx1391434680574433' and msource_type=1 ) or ( mobile='1391434680574433' and msource_type=1); +------+-------------+-----------+------+---------------+------+---------+------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +------+-------------+-----------+------+---------------+------+---------+------+-------+-------------+ | 1 | SIMPLE | m_db_vip | ALL | NULL | NULL | NULL | NULL | 86987 | Using where | +------+-------------+-----------+------+---------------+------+---------+------+-------+-------------+ 1 row in set (0.00 sec) MariaDB [db_vip]> show status like '%cost%'; +-----------------+--------------+ | Variable_name | Value | +-----------------+--------------+ | Last_query_cost | 18006.399000 | +-----------------+--------------+ 1 row in set (0.00 sec) 从执行计划中可以看出,这个SQL对表这个表m_db_vip进行了全表扫描,而表m_db_vip共有约10万行记录,Mysql优化器评估出的成本为18006, where条件的三列中msource_id与mobile都是选择性很强的列,msource_type的选择性弱, 首先对列msource_id创建一个索引: MariaDB [db_vip]> create index i_m_db_vip_1 on m_db_vip(msource_id); Query OK, 0 rows affected (1.18 sec) Records: 0 Duplicates: 0 Warnings: 0 再次执行SQL,发现Mysql并没有用上msource_id的索引(还是Oracle的CBO智能呀!) MariaDB [db_vip]> explain select ext_id, mid, msource_id, msource_type, referee, mobile, tel, mpassword,status from m_db_vip where (msource_id='xx1391434680574433' and msource_type=1 ) or ( mobile='1391434680574433' and msource_type=1); +------+-------------+-----------+------+---------------+------+---------+------+-------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +------+-------------+-----------+------+---------------+------+---------+------+-------+-------------+ | 1 | SIMPLE | m_db_vip | ALL | i_m_db_vip_1 | NULL | NULL | NULL | 86987 | Using where | +------+-------------+-----------+------+---------------+------+---------+------+-------+-------------+ 1 row in set (0.01 sec) MariaDB [db_vip]> show status like '%cost%'; +-----------------+--------------+ | Variable_name | Value | +-----------------+--------------+ | Last_query_cost | 18006.399000 | +-----------------+--------------+ 1 row in set (0.00 sec) 再创建mobile上的索引: MariaDB [db_vip]> create index i_m_db_vip_2 on m_db_vip(mobile); Query OK, 0 rows affected (0.96 sec) Records: 0 Duplicates: 0 Warnings: 0 MariaDB [db_vip]> explain select ext_id, mid, msource_id, msource_type, referee, mobile, tel, mpassword,status from m_db_vip where (msource_id='xx1391434680574433' and msource_type=1 ) or ( mobile='1391434680574433' and msource_type=1); +------+-------------+-----------+-------------+-----------------------------+-----------------------------+---------+------+------+-------------------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +------+-------------+-----------+-------------+-----------------------------+-----------------------------+---------+------+------+-------------------------------------------------------+ | 1 | SIMPLE | m_db_vip | index_merge | i_m_db_vip_1,i_m_db_vip_2 | i_m_db_vip_1,i_m_db_vip_2 | 98,99 | NULL | 2 | Using union(i_m_db_vip_1,i_m_db_vip_2); Using where | +------+-------------+-----------+-------------+-----------------------------+-----------------------------+---------+------+------+-------------------------------------------------------+ 1 row in set (0.02 sec) MariaDB [db_vip]> show status like '%cost%'; +-----------------+----------+ | Variable_name | Value | +-----------------+----------+ | Last_query_cost | 6.826060 | +-----------------+----------+ 1 row in set (0.00 sec) MariaDB [db_vip]>
    SQL的执行成本已经大幅降低了,经开发已测试,效果相当不错,并发从10几个冲到2000以上。
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