mysql查询优化相关技巧 用EXPLAIN语句检查优化器操作

  次阅读 来源:互联网(转载协议) 2016-01-27 15:49 我要评论(0)

使用EXPLAIN语句检查优化器操作 +----+-------------+----------+-------+---------------+------+---------+------+------+----------------- | id | select_type | table | type | possible_keys | key | key_len| ref | rows | Extra +----+-------------+----------+-------+---------------+------+---------+------+------+----------------- | 1 |SIMPLE | car_info | range | name | name | 768 | NULL | 9 | Using where; Using index | +----+-------------+----------+-------+---------------+------+---------+------+------+----------------

EXPLAIN输出解释

select_type 有如下几种类型: SIMPLE:未使用连接查询或者子查询的简单select语句 explain select * from car_info;

PRIMARY:最外层的select语句 explain select * from (select name from car_info where name like '凯迪拉克%') as a;

+----+-------------+------------+-------+---------------+------+---------+------+------+-------------

| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |

+----+-------------+------------+-------+---------------+------+---------+------+------+---------------

| 1 | PRIMARY | | ALL | NULL | NULL | NULL | NULL | 9 | |

| 2 | DERIVED | car_info | range | name | name | 768 | NULL | 9 | Using where; Using index |

+----+-------------+------------+-------+---------------+------+---------+------+------+---------------

UNION:union中的第二个,或后面的select语句 explain select name from car_info where id =100 union select name from web_car_brands where id =5; +------+--------------+----------------+-------+---------------+---------+---------+-------+------+-- | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +------+--------------+----------------+-------+---------------+---------+---------+-------+------+--- | 1 | PRIMARY | car_info | const | PRIMARY | PRIMARY | 8 | const | 1 | | | 2 | UNION | web_car_brands | const | PRIMARY,id | PRIMARY | 4 | const | 1 | | | NULL | UNION RESULT |

DEPENDENT UNION:union中的第二个或后面的色了传统语句,取决于外面的查询

mysql> explain select * from t3 where id in (select id from t3 where id=3952602 union all select id from t3) ;

+----+--------------------+------------+--------+-------------------+---------+---------+-------+------+------

| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |

+----+--------------------+------------+--------+-------------------+---------+---------+-------+------+--

| 1 | PRIMARY | t3 | ALL | NULL | NULL | NULL | NULL | 1000 | Using where

| 2 | DEPENDENT SUBQUERY | t3 | const | PRIMARY,idx_t3_id | PRIMARY | 4 | const | 1 | Using index |

| 3 | DEPENDENT UNION | t3 | eq_ref | PRIMARY,idx_t3_id | PRIMARY | 4 | func | 1 | Using where; Using index |

|NULL | UNION RESULT |

+----+--------------------+------------+--------+-------------------+---------+---------+-------+------+-

UNION RESULT:union的结果 explain select name from car_info where id =100 union select name from web_car_brands where id =5; +------+--------------+----------------+-------+---------------+---------+---------+-------+------+----- | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +------+--------------+----------------+-------+---------------+---------+---------+-------+------+-- | 1 | PRIMARY | car_info | const | PRIMARY | PRIMARY | 8 | const | 1 | | | 2 | UNION | web_car_brands | const | PRIMARY,id | PRIMARY | 4 | const | 1 | | | NULL | UNION RESULT |

SUBQUERY:子查询中的第一个SELECT语句 explain select name from car_info where id = (select id from web_car_series where id = 5); +----+-------------+----------------+-------+---------------+---------+---------+-------+------+----- | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------------+-------+---------------+---------+---------+-------+------+------ | 1 | PRIMARY | car_info | const | PRIMARY | PRIMARY | 8 | const | 1 | | | 2 | SUBQUERY | web_car_series | const | PRIMARY | PRIMARY | 4 | | 1 | Using index | +----+-------------+----------------+-------+---------------+---------+---------+-------+------+-----

本站部分文章来源于网络以及网友投稿,本站只负责对文章进行整理、排版、编辑,是出于传递更多信息之目的,并不意味着赞同其观点或证实其内容的真实性。如果您有什么意见或建议,请联系QQ28-1688-302!

人工智能实验室
相关文章相关文章
  • 第一批国家重点研发计划公布,旷视科技开启“五年行动”

    第一批国家重点研发计划公布,旷视科技开启“五年行动”

  • 品友互动为Digital Travel APAC2018 唯一受邀中国AI企业

    品友互动为Digital Travel APAC2018 唯一受邀中国AI企业

  • 让AI触手可及  Qualcomm携手创通联达推出全新终端侧AI开发套件

    让AI触手可及 Qualcomm携手创通联达推出全新终端侧AI开发套件

  • 长虹新款智能语音空调,告诉你空调也能玩Siri

    长虹新款智能语音空调,告诉你空调也能玩Siri

网友点评网友点评
阅读推荐阅读推荐

据外媒报道,STEER打造了首款完全自动驾驶停车技术,旨在使常规车辆转变为无人驾驶车辆。STEER的首款技术应用是4级自动驾驶及网络安全停车...

近日,美国软性机器抓手制造商 Soft Robotics 宣布,获得 2000 万美元的融资,本轮投资者包括 Scale Venture Partners,Calibrate Ventures...

据外媒报道,加州车管局发布了《2017自动驾驶脱离报告(California Autonomous Vehicle Disengagement Reports)》,其中谈及了脱离的具体...

用人机语音交互,来解决智能家居适老的问题;通过家庭门禁与安防套件、空气净化套件、可燃气体与有害气体监控套件等相互联动,在不同生活情...