| title | COLLATIONS |
|---|---|
| summary | 了解 information_schema 表 `COLLATIONS`。 |
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 | YES | | NULL | |
| IS_DEFAULT | varchar(3) | YES | | NULL | |
| IS_COMPILED | varchar(3) | YES | | NULL | |
| SORTLEN | bigint | YES | | NULL | |
| PAD_ATTRIBUTE | varchar(9) | YES | | NULL | |
+--------------------+-------------+------+------+---------+-------+
7 rows in set (0.001 sec)SELECT * FROM collations WHERE character_set_name='utf8mb4';+--------------------+--------------------+------+------------+-------------+---------+---------------+
| COLLATION_NAME | CHARACTER_SET_NAME | ID | IS_DEFAULT | IS_COMPILED | SORTLEN | PAD_ATTRIBUTE |
+--------------------+--------------------+------+------------+-------------+---------+---------------+
| utf8mb4_0900_ai_ci | utf8mb4 | 255 | | Yes | 0 | NO PAD |
| utf8mb4_0900_bin | utf8mb4 | 309 | | Yes | 1 | NO PAD |
| utf8mb4_bin | utf8mb4 | 46 | Yes | Yes | 1 | PAD SPACE |
| utf8mb4_general_ci | utf8mb4 | 45 | | Yes | 1 | PAD SPACE |
| utf8mb4_unicode_ci | utf8mb4 | 224 | | Yes | 8 | PAD SPACE |
+--------------------+--------------------+------+------------+-------------+---------+---------------+
5 rows in set (0.001 sec)COLLATIONS 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。PAD_ATTRIBUTE：在比较字符串时是否忽略末尾空格。PAD SPACE表示忽略末尾空格（例如'abc'等于'abc '），而NO PAD表示末尾空格会影响比较结果（例如'abc'不等于'abc '）。