??????????????????????????????????????? mysql的collation区分大小写设置

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????? 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.....

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mysql> select version();
+-----------+
| version() |
+-----------+
| 5.5.25    |
+-----------+
1 row in set (0.00 sec)

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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\

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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；

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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：

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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：

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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