MySQL多表join时报错如下:[Err]1267 – Illegal mix of collations(utf8_general_ci,IMPLICIT) and (utf8_unicode_ci,IMPLICIT) for operation ‘=
就是说两个表的排序规则(COLLATION)不同,无法完成比较。COLLATION是用在排序,大小比较上,一个字符集有一个或多种COLLATION,并且以_ci(大小写不敏感)、_cs(大小写敏感)或_bin(二进制)结束。在做比较时,应该确保两个表的字符排序相同。一般建表的时候不指定,可以走默认的,全是默认的就没什么问题了。
下面来模拟一下各种场景,表结构如下(utf8默认排序规则为utf8_general_ci):
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mysql> show create table test.cs\G *************************** 1. row *************************** Table : cs Create Table : CREATE TABLE `cs` ( `id` int (11) DEFAULT NULL , ` name ` varchar (10) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8 1 row in set (0.01 sec) |
查看表默认排序规则集
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mysql> select TABLE_SCHEMA,TABLE_NAME,TABLE_COLLATION from information_schema.tables where table_name= 'cs' ; + --------------+------------+-----------------+ | TABLE_SCHEMA | TABLE_NAME | TABLE_COLLATION | + --------------+------------+-----------------+ | test | cs | utf8_general_ci | + --------------+------------+-----------------+ 1 row in set (0.00 sec) |
查看列排序规则集
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mysql> select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,COLLATION_NAME from information_schema.COLUMNS where TABLE_NAME= 'cs' ; + --------------+------------+-------------+-----------------+ | TABLE_SCHEMA | TABLE_NAME | COLUMN_NAME | COLLATION_NAME | + --------------+------------+-------------+-----------------+ | test | cs | id | NULL | | test | cs | name | utf8_general_ci | + --------------+------------+-------------+-----------------+ 2 rows in set (0.00 sec) |
从utf8升级为utf8mb4是不支持online ddl的,如下:
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mysql> ALTER TABLE cs CONVERT TO CHARACTER SET utf8mb4,ALGORITHM=INPLACE,LOCK=NONE; ERROR 1846 (0A000): ALGORITHM=INPLACE is not supported. Reason: Cannot change column type INPLACE. Try ALGORITHM=COPY. |
从utf8.utf8_general_ci变更为utf8.utf8_unicode_ci是不支持online ddl的,如下:
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mysql> ALTER TABLE cs CONVERT TO CHARACTER SET utf8 collate utf8_unicode_ci,ALGORITHM=INPLACE,LOCK=NONE; ERROR 1846 (0A000): ALGORITHM=INPLACE is not supported. Reason: Cannot change column type INPLACE. Try ALGORITHM=COPY. |
如果使用下面这种方式修改字符集,你会发现,只更改了表级的,没有更改列级的。
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mysql> ALTER TABLE cs CHARACTER SET utf8 collate utf8_unicode_ci; Query OK, 0 rows affected (0.01 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> select TABLE_SCHEMA,TABLE_NAME,TABLE_COLLATION from information_schema.tables where table_name= 'cs' ; + --------------+------------+-----------------+ | TABLE_SCHEMA | TABLE_NAME | TABLE_COLLATION | + --------------+------------+-----------------+ | test | cs | utf8_unicode_ci | + --------------+------------+-----------------+ 1 row in set (0.00 sec) mysql> select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,COLLATION_NAME from information_schema.COLUMNS where TABLE_NAME= 'cs' ; + --------------+------------+-------------+-----------------+ | TABLE_SCHEMA | TABLE_NAME | COLUMN_NAME | COLLATION_NAME | + --------------+------------+-------------+-----------------+ | test | cs | id | NULL | | test | cs | name | utf8_general_ci | + --------------+------------+-------------+-----------------+ 2 rows in set (0.00 sec) |
所以真正改字符集的时候别忘了加上CONVERT TO,如下:
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mysql> ALTER TABLE cs CONVERT TO CHARACTER SET utf8 collate utf8_unicode_ci; Query OK, 5 rows affected (0.06 sec) Records: 5 Duplicates: 0 Warnings: 0 mysql> select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,COLLATION_NAME from information_schema.COLUMNS where TABLE_NAME= 'cs' ; + --------------+------------+-------------+-----------------+ | TABLE_SCHEMA | TABLE_NAME | COLUMN_NAME | COLLATION_NAME | + --------------+------------+-------------+-----------------+ | test | cs | id | NULL | | test | cs | name | utf8_unicode_ci | + --------------+------------+-------------+-----------------+ 2 rows in set (0.00 sec) |
要仅仅改变一个表的默认字符集,应使用此语句:
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mysql> ALTER TABLE cs default CHARACTER SET utf8 collate utf8_general_ci,ALGORITHM=INPLACE,LOCK=NONE; Query OK, 0 rows affected (0.00 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> select TABLE_SCHEMA,TABLE_NAME,TABLE_COLLATION from information_schema.tables where table_name= 'cs' ; + --------------+------------+-----------------+ | TABLE_SCHEMA | TABLE_NAME | TABLE_COLLATION | + --------------+------------+-----------------+ | test | cs | utf8_general_ci | + --------------+------------+-----------------+ 1 row in set (0.00 sec) mysql> select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,COLLATION_NAME from information_schema.COLUMNS where TABLE_NAME= 'cs' ; + --------------+------------+-------------+-----------------+ | TABLE_SCHEMA | TABLE_NAME | COLUMN_NAME | COLLATION_NAME | + --------------+------------+-------------+-----------------+ | test | cs | id | NULL | | test | cs | name | utf8_unicode_ci | + --------------+------------+-------------+-----------------+ 2 rows in set (0.00 sec) |
可以发现列字符集没有改变,并且只有新的列才会默认继承表的字符集(utf8.utf8_general_ci)。
总结
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