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下面是测试用例,楼主的测试使用的MySQL版本是5.6.27-log。
show create table user_man;
CREATE TABLE `user_man` ( `manid` bigint(20) NOT NULL AUTO_INCREMENT, `manname` varchar(32) DEFAULT NULL, `manage` int(6) DEFAULT NULL, `upd_time` timestamp NOT NULL DEFAULT '2000-01-01 00:00:00' ON UPDATE CURRENT_TIMESTAMP, `blacklist` bigint(20) DEFAULT '-1' COMMENT '-1,1', PRIMARY KEY (`manid`), KEY `IDX_MN` (`manname`) USING BTREE, KEY `IDX_MID` (`manid`) USING BTREE ) ENGINE=InnoDB AUTO_INCREMENT=23 DEFAULT CHARSET=utf8; show create table user_woman; CREATE TABLE `user_woman` ( `womanid` int(11) NOT NULL AUTO_INCREMENT, `womanname` varchar(20) DEFAULT NULL, `womanage` int(6) DEFAULT NULL, PRIMARY KEY (`womanid`) ) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8; #执行计划中type定义说明: #(1)执行计划type为ALL:遍历全表来查找 explain SELECT * from user_man ; explain select * from user_man where manage in (9,10);#非索引范围查找也是走全表 #(2)执行计划type为index:只遍历索引树 explain SELECT manid from user_man; #(3)执行计划type为range:索引扫描范围 explain select *from user_man where manid < 10; explain select * from user_man where manid in (8,10,9) order by manage; #(4)执行计划type为ref:非唯一性扫描索引 explain select *from user_man where manname = 'zzk'; #(5) 执行计划type为eq_ref:唯一性索引扫描 explain select * from user_man ,user_woman where user_man.manid = user_woman.womanid; explain select * from user_man where manid in (select womanid from user_woman); #(6)执行计划type为const、system:当MySQL对查询某部分进行优化,并转换为一个常量时,使用这些类型访问。如将主键置于where列表中,MySQL就能将该查询转换为一个常量 explain select *from user_man where manid = 8; explain select * from (select * from user_man where manid=8) dd; #(7)NULL:MySQL在优化过程中分解语句,执行时甚至不用访问表或索引 explain select * from user_man where manid = (select min(womanid) from user_woman) #查询中若使用了覆盖索引,则该索引仅出现在key列表中(为manid、manname建立了索引,单独查这两个字段); explain select manid ,manname from user_man where manname = 'zzzz' and manage = 43;转载地址:http://pqnqb.baihongyu.com/