Question

COLLATIONS 表提供了 CHARACTER_SETS 表中字符集对应的排序规则列表。目前 TiDB 包含该表仅为兼容 MySQL。

USE information_schema;
DESC collations;

+--------------------+-------------+------+------+---------+-------+
| Field              | Type        | Null | Key  | Default | Extra |
+--------------------+-------------+------+------+---------+-------+
| COLLATION_NAME     | varchar(32) | YES  |      | NULL    |       |
| CHARACTER_SET_NAME | varchar(32) | YES  |      | NULL    |       |
| ID                 | bigint(11)  | YES  |      | NULL    |       |
| IS_DEFAULT         | varchar(3)  | YES  |      | NULL    |       |
| IS_COMPILED        | varchar(3)  | YES  |      | NULL    |       |
| SORTLEN            | bigint(3)   | YES  |      | NULL    |       |
+--------------------+-------------+------+------+---------+-------+
6 rows in set (0.00 sec)

SELECT * FROM collations WHERE character_set_name='utf8mb4';

+----------------+--------------------+------+------------+-------------+---------+
| COLLATION_NAME | CHARACTER_SET_NAME | ID   | IS_DEFAULT | IS_COMPILED | SORTLEN |
+----------------+--------------------+------+------------+-------------+---------+
| utf8mb4_bin    | utf8mb4            |   46 | Yes        | Yes         |       1 |
+----------------+--------------------+------+------------+-------------+---------+
1 row in set (0.00 sec)

COLLATION 表中列的含义如下：

• COLLATION_NAME：排序规则名称
• CHARACTER_SET_NAME：排序规则所属的字符集名称
• ID：排序规则的 ID
• IS_DEFAULT：该排序规则是否是所属字符集的默认排序规则
• IS_COMPILED：字符集是否编译到服务器中
• SORTLEN：排序规则在对字符进行排序时，所分配内存的最小长度