# 字符集和排序规则

__*字符集*__

__*排序规则*__

+ `Character Set` 是一组符号和编码。
  + 所有字符串都属于一个特定的字符集
  + TiDB 中的默认字符集是 utf8mb4
+ `Collation` 是一组用于比较字符集中字符和字符排序顺序的规则
  + 影响字符和字符串的比较
  + TiDB 中的默认的规则是 utf8mb4_bin
+ `SHOW CHARACTER SET`:显示所有支持的字符集
+ `SHOW COLLATION`:显示所有支持的排序规则
-------------------------------------------------------------------------------------

```
tidb> show character set;
+---------+-------------------------------------+-------------------+--------+
| Charset | Description                         | Default collation | Maxlen |
+---------+-------------------------------------+-------------------+--------+
| ascii   | US ASCII                            | ascii_bin         |      1 |
| binary  | binary                              | binary            |      1 |
| gbk     | Chinese Internal Code Specification | gbk_chinese_ci    |      2 |
| latin1  | Latin1                              | latin1_bin        |      1 |
| utf8    | UTF-8 Unicode                       | utf8_bin          |      3 |
| utf8mb4 | UTF-8 Unicode                       | utf8mb4_bin       |      4 |
+---------+-------------------------------------+-------------------+--------+
6 rows in set (0.01 sec)

tidb> show collation;
+--------------------+---------+------+---------+----------+---------+
| Collation          | Charset | Id   | Default | Compiled | Sortlen |
+--------------------+---------+------+---------+----------+---------+
| ascii_bin          | ascii   |   65 | Yes     | Yes      |       1 |
| binary             | binary  |   63 | Yes     | Yes      |       1 |
| gbk_bin            | gbk     |   87 |         | Yes      |       1 |
| gbk_chinese_ci     | gbk     |   28 | Yes     | Yes      |       1 |
| latin1_bin         | latin1  |   47 | Yes     | Yes      |       1 |
| utf8_bin           | utf8    |   83 | Yes     | Yes      |       1 |
| utf8_general_ci    | utf8    |   33 |         | Yes      |       1 |
| utf8_unicode_ci    | utf8    |  192 |         | Yes      |       1 |
| utf8mb4_bin        | utf8mb4 |   46 | Yes     | Yes      |       1 |
| utf8mb4_general_ci | utf8mb4 |   45 |         | Yes      |       1 |
| utf8mb4_unicode_ci | utf8mb4 |  224 |         | Yes      |       1 |
+--------------------+---------+------+---------+----------+---------+
11 rows in set (0.00 sec)

tidb> select 'A'='a' collate utf8mb4_bin, 'A'='a' collate utf8mb4_general_ci, 'A'='a';
+-----------------------------+------------------------------------+---------+
| 'A'='a' collate utf8mb4_bin | 'A'='a' collate utf8mb4_general_ci | 'A'='a' |
+-----------------------------+------------------------------------+---------+
|                           0 |                                  1 |       0 |
+-----------------------------+------------------------------------+---------+
1 row in set (0.00 sec)
```