mysql的collation区分大小写设置
mysql数据库在做查询时候，有时候是英文字母大小写敏感的，有时候又不是的，主要是由于mysql的字符校验规则的设置。通常默认是不支持的大小写字母敏感的，在主动设置mysql数据库的collation后，可以使得数据库满足大小写敏感，适合客户的一定要求。通过下面的试验进行理解学习.....
mysql> select version(); +-----------+ | version() | +-----------+ | 5.5.25 | +-----------+ 1 row in set (0.00 sec)
mysql> show variables like '%character%'; +--------------------------+------------------------------------------------------- | Variable_name | Value +--------------------------+------------------------------------------------------- | character_set_client | utf8 | character_set_connection | utf8 | character_set_database | latin1 | character_set_filesystem | binary | character_set_results | utf8 | character_set_server | latin1 | character_set_system | utf8 | character_sets_dir | D:\database\mysql\mysql-5.5.25-winx64\share\charsets\
mysql> show variables like '%collation%'; +----------------------+-------------------+ | Variable_name | Value | +----------------------+-------------------+ | collation_connection | utf8_general_ci | | collation_database | latin1_swedish_ci | | collation_server | latin1_swedish_ci | +----------------------+-------------------+ 3 rows in set (0.00 sec)
默认即为：collation_connection = utf8_general_ci 大小写不敏感校验规则；
mysql> show collation like '%utf8%'; +--------------------------+---------+-----+---------+----------+---------+ | Collation | Charset | Id | Default | Compiled | Sortlen | +--------------------------+---------+-----+---------+----------+---------+ | utf8_general_ci | utf8 | 33 | Yes | Yes | 1 | | utf8_bin | utf8 | 83 | | Yes | 1 | | utf8_unicode_ci | utf8 | 192 | | Yes | 8 | | utf8_icelandic_ci | utf8 | 193 | | Yes | 8 |
客户端字符集：utf8, 校验规则: utf8_general_ci, 默认为yes，即不是大小写敏感的匹配；
而utf8_bin是区分大小写的校验规则；
创建表做测试，看数据效果：
mysql> create table T_collation(first varchar(30) character set utf8
-> collate utf8_bin,second varchar(30) character set utf8 collate
-> utf8_general_ci);
Query OK, 0 rows affected (0.32 sec)
mysql> show create table t_collation\G;
*************************** 1. row ***************************
Table: t_collation
Create Table: CREATE TABLE `t_collation` (
`first` varchar(30) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
`second` varchar(30) CHARACTER SET utf8 DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
ERROR:
No query specified
mysql> insert into t_collation values('M','M'),('N','N'),('a','a'),('b','b');
Query OK, 4 rows affected (0.13 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from t_collation;
+-------+--------+
| first | second |
+-------+--------+
| M | M |
| N | N |
| a | a |
| b | b |
+-------+--------+
4 rows in set (0.00 sec)
比较查询结果：
mysql> insert into t_collation values('m','m'),('n','n');
Query OK, 2 rows affected (0.10 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from t_collation;
+-------+--------+
| first | second |
+-------+--------+
| M | M |
| N | N |
| a | a |
| b | b |
| m | m |
| n | n |
+-------+--------+
6 rows in set (0.00 sec)
mysql> select * from t_collation where first='m';
+-------+--------+
| first | second |
+-------+--------+
| m | m |
+-------+--------+
1 row in set (0.02 sec)
mysql> select * from t_collation where second='m';
+-------+--------+
| first | second |
+-------+--------+
| M | M |
| m | m |
+-------+--------+
2 rows in set (0.00 sec)
mysql> select * from t_collation where second='M';
+-------+--------+
| first | second |
+-------+--------+
| M | M |
| m | m |
+-------+--------+
2 rows in set (0.00 sec)
mysql> select * from t_collation where first='M';
+-------+--------+
| first | second |
+-------+--------+
| M | M |
+-------+--------+
1 row in set (0.00 sec)
比较各自的校验规则，utf8_bin是区分大小写的，而utf8_general_ci是不区分的，默认的。
还可以从排序语句中进行比较，看看测试效果的.....
mysql> select * from t_collation; +-------+--------+ | first | second | +-------+--------+ | M | M | | N | N | | a | a | | b | b | | m | m | | n | n | +-------+--------+ 6 rows in set (0.00 sec) mysql> select * from t_collation order by first; +-------+--------+ | first | second | +-------+--------+ | M | M | | N | N | | a | a | | b | b | | m | m | | n | n | +-------+--------+ 6 rows in set (0.00 sec) mysql> select * from t_collation order by second; +-------+--------+ | first | second | +-------+--------+ | a | a | | b | b | | M | M | | m | m | | N | N | | n | n | +-------+--------+ 6 rows in set (0.00 sec)
同样符合校验规则的检查。
结论： 在MYSQL数据库中，根据实际业务需要，适当可以调整字符集的(collation)校验规则，修改默认的大小写敏感问题，满足实际需要，这本身就是数据库的一种设置，熟悉标准、规则，适当利用为项目所用，可以针对具体的数据库或者表或者表的列进行设置。