mysql varchar int 123 走索引吗?,
结论:
当MySQL中字段为int类型时,搜索条件where num='111' 与where num=111都可以使用该字段的索引。
当MySQL中字段为varchar类型时,搜索条件where num='111' 可以使用索引,where num=111 不可以使用索引
验证过程:
建表语句:
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CREATE TABLE `gyl` (
`id` int (11) NOT NULL AUTO_INCREMENT,
`str` varchar (255) NOT NULL ,
`num` int (11) NOT NULL DEFAULT '0' ,
`obj` varchar (255) DEFAULT NULL ,
PRIMARY KEY (`id`),
KEY `str_x` (`str`),
KEY `num_x` (`num`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
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向表中使用自复制语句插入数据
insert into gyl (`str`,`num`)values(123123,'12313');
insert into gyl (`str`,`num`) select `str`,`num` from gyl;
更改数据 update gyl set num=id,str=id
结果:
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mysql> explain
select * from gyl where str=123123 limit 1;
+ ----+-------------+-------+------+---------------+------+---------+------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+ ----+-------------+-------+------+---------------+------+---------+------+--------+-------------+
| 1 | SIMPLE | gyl | ALL | str_x | NULL | NULL | NULL | 262756 | Using where |
+ ----+-------------+-------+------+---------------+------+---------+------+--------+-------------+
1 row in set
mysql> explain select * from gyl where str= '123123' limit 1;
+ ----+-------------+-------+------+---------------+-------+---------+-------+--------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+ ----+-------------+-------+------+---------------+-------+---------+-------+--------+-------------+
| 1 | SIMPLE | gyl | ref | str_x | str_x | 257 | const | 131378 | Using where |
+ ----+-------------+-------+------+---------------+-------+---------+-------+--------+-------------+
1 row in set
mysql> explain select * from gyl where num= '12313' limit 1;;
+ ----+-------------+-------+------+---------------+-------+---------+-------+--------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+ ----+-------------+-------+------+---------------+-------+---------+-------+--------+-------+
| 1 | SIMPLE | gyl | ref | num_x | num_x | 4 | const | 131378 | |
+ ----+-------------+-------+------+---------------+-------+---------+-------+--------+-------+
1 row in set
1065 - Query was empty
mysql> explain select * from gyl where num=12313 limit 1;
+ ----+-------------+-------+------+---------------+-------+---------+-------+--------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+ ----+-------------+-------+------+---------------+-------+---------+-------+--------+-------+
| 1 | SIMPLE | gyl | ref | num_x | num_x | 4 | const | 131378 | |
+ ----+-------------+-------+------+---------------+-------+---------+-------+--------+-------+
1 row in set
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