Alter table default character set 修改 MySQL 5.6 中的行
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【中文标题】Alter table default character set 修改 MySQL 5.6 中的行【英文标题】:Alter table default character set modifies the rows in MySQL 5.6 【发布时间】:2019-07-05 07:20:55 【问题描述】:我使用的是 mysql 5.6,我想修改一个表的默认编码(从 latin1 到 utf8),而不修改现有的列和行。 基于documentation,我尝试了以下命令:
ALTER TABLE mytable DEFAULT CHARACTER SET utf8;
它修改了我的表的默认字符集编码,并没有像预期的那样修改列的排序规则,但我真的很惊讶地看到:
Query OK, 32141 rows affected (6.31 sec)
Records: 32141 Duplicates: 0 Warnings: 0
除了“32141 行受影响”之外,结果与您预期的一样,如下所示:
MySQL> select count(*) from mytable;
+----------+
| count(*) |
+----------+
| 32141 |
+----------+
1 row in set (0.01 sec)
MySQL> show table status like 'mytable';
+-----------------------+--------+---------+------------+-------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+-----------------------+--------+---------+------------+-------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------------+----------+----------------+---------+
| mytable | InnoDB | 10 | Compact | 16723 | 20798 | 347815936 | 0 | 21561344 | 15728640 | NULL | NULL | NULL | NULL | utf8_general_ci | NULL | partitioned | |
+-----------------------+--------+---------+------------+-------+----------------+-------------+-----------------+--------------+-----------+----------------+-------------+-------------+------------+-----------------+----------+----------------+---------+
MySQL> show create table mytable;
CREATE TABLE `mytable` (
`ID` varchar(255) NOT NULL,
`COL1` double DEFAULT NULL,
`COL2` longtext CHARACTER SET latin1,
`COL3` datetime DEFAULT NULL,
`COL4` varchar(255) CHARACTER SET latin1 DEFAULT NULL,
`COL5` int(11) DEFAULT NULL,
`COL6` datetime DEFAULT NULL,
`COL7` varchar(255) CHARACTER SET latin1 DEFAULT NULL,
`COL8` datetime(3) NOT NULL,
`COL9` int(11) NOT NULL DEFAULT '-1',
`COL10` int(11) DEFAULT '0',
`COL11` double DEFAULT '0',
PRIMARY KEY (`ID`,`COL9`),
KEY `idx1` (`COL7`,`COL3`,`COL6`),
KEY `idx2` (`COL1`,`COL4`,`COL3`,`COL6`),
KEY `idx3` (`ID`,`COL3`,`COL6`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
/*!50100 PARTITION BY RANGE (`COL9`)
(PARTITION p0 VALUES LESS THAN (1) ENGINE = InnoDB,
PARTITION p1 VALUES LESS THAN (2) ENGINE = InnoDB,
PARTITION p2 VALUES LESS THAN (3) ENGINE = InnoDB,
PARTITION p3 VALUES LESS THAN (4) ENGINE = InnoDB,
PARTITION p4 VALUES LESS THAN (5) ENGINE = InnoDB,
PARTITION p5 VALUES LESS THAN (6) ENGINE = InnoDB,
PARTITION p6 VALUES LESS THAN (7) ENGINE = InnoDB,
PARTITION p7 VALUES LESS THAN (8) ENGINE = InnoDB,
PARTITION p8 VALUES LESS THAN (9) ENGINE = InnoDB,
PARTITION p9 VALUES LESS THAN (10) ENGINE = InnoDB,
PARTITION p10 VALUES LESS THAN (11) ENGINE = InnoDB,
PARTITION p11 VALUES LESS THAN (100) ENGINE = InnoDB,
PARTITION p12 VALUES LESS THAN (101) ENGINE = InnoDB,
PARTITION p13 VALUES LESS THAN (102) ENGINE = InnoDB,
PARTITION p14 VALUES LESS THAN (103) ENGINE = InnoDB,
PARTITION p15 VALUES LESS THAN (104) ENGINE = InnoDB,
PARTITION p16 VALUES LESS THAN (105) ENGINE = InnoDB,
PARTITION p17 VALUES LESS THAN (106) ENGINE = InnoDB,
PARTITION p18 VALUES LESS THAN (107) ENGINE = InnoDB,
PARTITION p19 VALUES LESS THAN (108) ENGINE = InnoDB,
PARTITION p20 VALUES LESS THAN (109) ENGINE = InnoDB,
PARTITION p21 VALUES LESS THAN (110) ENGINE = InnoDB,
PARTITION p22 VALUES LESS THAN (111) ENGINE = InnoDB,
PARTITION p23 VALUES LESS THAN (200) ENGINE = InnoDB,
PARTITION p24 VALUES LESS THAN (201) ENGINE = InnoDB,
PARTITION p25 VALUES LESS THAN (202) ENGINE = InnoDB,
PARTITION p26 VALUES LESS THAN (203) ENGINE = InnoDB,
PARTITION p27 VALUES LESS THAN (204) ENGINE = InnoDB,
PARTITION p28 VALUES LESS THAN (205) ENGINE = InnoDB,
PARTITION p29 VALUES LESS THAN (206) ENGINE = InnoDB,
PARTITION p30 VALUES LESS THAN (207) ENGINE = InnoDB,
PARTITION p31 VALUES LESS THAN (208) ENGINE = InnoDB,
PARTITION p32 VALUES LESS THAN (209) ENGINE = InnoDB,
PARTITION p33 VALUES LESS THAN (210) ENGINE = InnoDB,
PARTITION p34 VALUES LESS THAN (211) ENGINE = InnoDB,
PARTITION p35 VALUES LESS THAN MAXVALUE ENGINE = InnoDB) */
MySQL> show full columns from mytable;
+--------------------------+--------------+-------------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type | Collation | Null | Key | Default | Extra | Privileges | Comment |
+--------------------------+--------------+-------------------+------+-----+---------+-------+---------------------------------+---------+
| ID | varchar(255) | latin1_swedish_ci | NO | PRI | NULL | | select,insert,update,references | |
| COL1 | double | NULL | YES | MUL | NULL | | select,insert,update,references | |
| COL2 | longtext | latin1_swedish_ci | YES | | NULL | | select,insert,update,references | |
| COL3 | datetime | NULL | YES | | NULL | | select,insert,update,references | |
| COL4 | varchar(255) | latin1_swedish_ci | YES | | NULL | | select,insert,update,references | |
| COL5 | int(11) | NULL | YES | | NULL | | select,insert,update,references | |
| COL6 | datetime | NULL | YES | | NULL | | select,insert,update,references | |
| COL7 | varchar(255) | latin1_swedish_ci | YES | MUL | NULL | | select,insert,update,references | |
| COL8 | datetime(3) | NULL | NO | | NULL | | select,insert,update,references | |
| COL9 | int(11) | NULL | NO | PRI | -1 | | select,insert,update,references | |
| COL10 | int(11) | NULL | YES | | 0 | | select,insert,update,references | |
| COL11 | double | NULL | YES | | 0 | | select,insert,update,references | |
+--------------------------+--------------+-------------------+------+-----+---------+-------+---------------------------------+---------+
我的连接参数如下:
MySQL> show variables where variable_name like '%char%' or variable_name like '%collation%';
+--------------------------+--------------------------------------------------+
| Variable_name | Value |
+--------------------------+--------------------------------------------------+
| character_set_client | utf8mb4 |
| character_set_connection | utf8mb4 |
| character_set_database | utf8mb4 |
| character_set_filesystem | binary |
| character_set_results | utf8mb4 |
| character_set_server | utf8mb4 |
| character_set_system | utf8 |
| collation_connection | utf8mb4_general_ci |
| collation_database | utf8mb4_general_ci |
| collation_server | utf8mb4_general_ci |
+--------------------------+--------------------------------------------------+
注意:
数据是从 Java 应用程序创建的 在创建数据时,连接参数设置为utf8 没有与此表链接的 FK当我尝试使用一些新创建的表进行重现时,似乎没有修改行。见下文“0行受影响”:
MySQL> select count(*) from mytesttable;
+----------+
| count(*) |
+----------+
| 3 |
+----------+
3 row in set (0.10 sec)
MySQL> alter table mytesttable character set utf8;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
我在数据创建过程中尝试将连接参数改回 latin1,但结果没有改变:仍然“0 行受影响”。
所以我的问题:
-
我对命令的理解是否正确? (它不应该修改行)
什么可以解释在第一种情况下行受到影响?
编辑
我刚刚发现,如果我删除分区,问题就不会发生。
-
使用分区我得到“XXX 受影响的行”
如果没有分区,我会得到“0 个受影响的行”
这是预期的吗?
用摘要编辑 2
最初:
-
该表使用
latin1
作为默认编码(列相同)
连接被声明为utf8
什么有效:
-
在任何
ALTER TABLE
命令之前,像“é”这样的字符似乎是latin1
编码的(E9
)
运行命令ALTER TABLE mytable CHARACTER SET utf8mb4;
不修改数据(十六进制命令仍显示E9
)
列仍声明为latin1
。
运行命令ALTER TABLE mytable MODIFY COL2 LONGTEXT CHARACTER SET utf8mb4
将列 更改为utf8mb4
(C3A9
)
到目前为止一切顺利。
剩下的问题:
-
如何确保表中的所有数据都是
latin1
?我试过SELECT COL2 FROM mytable WHERE LENGTH(COL2) != CHAR_LENGTH(COL2) LIMIT 1
,我得到了 0 个结果。够了吗?
为什么命令ALTER TABLE mytable CHARACTER SET utf8mb4;
显示
“32141 行受影响”似乎数据没有被修改?
(当表在同一列上有分区和索引时会发生这种情况)
根据前一点,更改表的默认编码是否安全(需要?)?还是我应该坚持修改列?
非常感谢您的帮助
【问题讨论】:
数据看起来真的变了吗? 嗨@deceze,感谢您抽出宝贵的时间。它似乎没有改变,但我不确定我是否尝试了好的命令。我在备份表和修改后的表上都尝试了select * from mytable limit 1;
和select hex(COL1), hex(COL2)... from mytable limit 1;
,我得到了相同的结果。我也尝试了提到的命令here,但它没有给我任何结果
在mytesttable
中,有CHAR
或TEXT
的列吗? SHOW CREATE TABLE mytesttable
在 ALTER
之前说了什么?
您觉得PARTITIONing
有什么好处吗? (我对此表示怀疑。)
让我们看看HEX()
一个带有重音字母的单元格。你可能有“双重编码”而没有意识到。
【参考方案1】:
你搞砸了,ALTER
让事情变得更糟。
首先,表列被声明为latin1
并且连接声明客户端正在使用latin1
(通过SET NAMES latin1
)。如果é
在客户端中实际上是十六进制的E9
,那会很好。但是客户端中的数据是UTF-8。所以 é
是两个字节 C3A9
作为 2 个 latin1 字符发送到数据库。损坏并不明显,因为当你SELECTed
时它被逆转了。
后面的步骤将这些字节中的 每个 视为 latin1 并将它们转换为 utf8,从而使事情变得混乱,因此是“双重”编码。
请参阅 Trouble with UTF-8 characters; what I see is not what I stored 中的“Mojibake”和“双重编码”。如果您想尝试恢复数据,请参阅http://mysql.rjweb.org/doc.php/charcoll#fixes_for_various_cases中的相应案例
嗯,显然ALTER TABLE mytable DEFAULT CHARACTER SET utf8;
不仅仅是更改默认值,而是复制表格,并在这样做时引入了双重编码。
十多年来,我一直在研究 MySQL 字符集问题。这是我还没有观察到的新皱纹。
我很确定character_set_system
与您的问题无关。 (但我可能是错的!)
错误的设置名称
测试用例:
CREATE TABLE mytest ( MYDATA longtext ) ENGINE=InnoDB DEFAULT CHARSET=latin1;
SET NAMES latin1;
INSERT INTO mytest VALUES ( "é" );
SELECT MYDATA, HEX(MYDATA) FROM mytest;
运行该测试用例:
mysql> SET NAMES latin1;
mysql> SHOW CREATE TABLE mytest\G
*************************** 1. row ***************************
Table: mytest
Create Table: CREATE TABLE `mytest` (
`MYDATA` longtext
) ENGINE=InnoDB DEFAULT CHARSET=latin1
mysql> INSERT INTO mytest VALUES ( "é" );
mysql> SELECT MYDATA, HEX(MYDATA), LENGTH(MYDATA),
CHAR_LENGTH(MYDATA) FROM mytest;
+--------+-------------+----------------+---------------------+
| MYDATA | HEX(MYDATA) | LENGTH(MYDATA) | CHAR_LENGTH(MYDATA) |
+--------+-------------+----------------+---------------------+
| é | C3A9 | 2 | 2 |
+--------+-------------+----------------+---------------------+
角色看起来不错。但是 HEX 看起来像 UTF-8,而不是 latin1。而CHAR_LENGTH
是“错误的”。
案例是:CHARACTER SET latin1
,但是里面有utf8字节。
在修复字符集时不处理字节:
然后在不改变字节的情况下转换列:
ALTER TABLE tbl MODIFY COLUMN MYDATA LONGBLOB;
ALTER TABLE tbl MODIFY COLUMN MYDATA LONGTEXT CHARACTER SET utf8mb4;
(确保拥有你原来拥有的所有属性,例如NOT NULL
。)
这是“2 步 ALTER”,如 http://mysql.rjweb.org/doc.php/charcoll 中所述。)(确保其他规范保持不变 - VARCHAR、NOT NULL 等)
分区测试用例:
DROP TABLE IF EXISTS ptest;
CREATE TABLE ptest (
nn INT NOT NULL,
ee LONGTEXT
) ENGINE=InnoDB DEFAULT CHARSET=latin1
PARTITION BY RANGE (nn)
(PARTITION p0 VALUES LESS THAN (1),
PARTITION p1 VALUES LESS THAN MAXVALUE);
SET NAMES latin1;
INSERT INTO ptest (nn, ee) VALUES ( 0, "é" ), ( 1, "ü" );
SELECT nn, ee, HEX(ee), LENGTH(ee), CHAR_LENGTH(ee) FROM ptest;
ALTER TABLE ptest
DEFAULT CHARSET utf8;
SELECT nn, ee, HEX(ee), LENGTH(ee), CHAR_LENGTH(ee) FROM ptest;
SELECT @@version;
SHOW CREATE TABLE ptest\G
分区结果:
mysql> DROP TABLE IF EXISTS ptest;
Query OK, 0 rows affected (0.02 sec)
mysql> CREATE TABLE ptest (
-> nn INT NOT NULL,
-> ee LONGTEXT
-> ) ENGINE=InnoDB DEFAULT CHARSET=latin1
-> PARTITION BY RANGE (nn)
-> (PARTITION p0 VALUES LESS THAN (1),
-> PARTITION p1 VALUES LESS THAN MAXVALUE);
Query OK, 0 rows affected (0.03 sec)
mysql> SET NAMES latin1;
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO ptest (nn, ee) VALUES ( 0, "é" ), ( 1, "ü" );
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> SELECT nn, ee, HEX(ee), LENGTH(ee), CHAR_LENGTH(ee) FROM ptest;
+----+------+---------+------------+-----------------+
| nn | ee | HEX(ee) | LENGTH(ee) | CHAR_LENGTH(ee) |
+----+------+---------+------------+-----------------+
| 0 | é | C3A9 | 2 | 2 |
| 1 | ü | C3BC | 2 | 2 |
+----+------+---------+------------+-----------------+
2 rows in set (0.00 sec)
mysql> ALTER TABLE ptest
-> DEFAULT CHARSET utf8;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> SELECT nn, ee, HEX(ee), LENGTH(ee), CHAR_LENGTH(ee) FROM ptest;
+----+------+---------+------------+-----------------+
| nn | ee | HEX(ee) | LENGTH(ee) | CHAR_LENGTH(ee) |
+----+------+---------+------------+-----------------+
| 0 | é | C3A9 | 2 | 2 |
| 1 | ü | C3BC | 2 | 2 |
+----+------+---------+------------+-----------------+
2 rows in set (0.00 sec)
mysql> SELECT @@version;
+-----------------+
| @@version |
+-----------------+
| 5.6.22-71.0-log |
+-----------------+
1 row in set (0.00 sec)
mysql> SHOW CREATE TABLE ptest\G
*************************** 1. row ***************************
Table: ptest
Create Table: CREATE TABLE `ptest` (
`nn` int(11) NOT NULL,
`ee` longtext CHARACTER SET latin1
) ENGINE=InnoDB DEFAULT CHARSET=utf8
/*!50100 PARTITION BY RANGE (nn)
(PARTITION p0 VALUES LESS THAN (1) ENGINE = InnoDB,
PARTITION p1 VALUES LESS THAN MAXVALUE ENGINE = InnoDB) */
1 row in set (0.00 sec)
嗯...我没有看到 ALTER 问题。你用的是什么版本?你看到这个测试用例的问题了吗?
【讨论】:
ALTER TABLE mytable DEFAULT CHARACTER SET utf8;
不会更改十六进制值。这是更改十六进制值的ALTER TABLE ... MODIFY COL2 ...
。我先用set NAMES utf8
再试了一次。在这种情况下,我得到: E96CE96D656E7473
(latin1) 在任何 ALTER
命令之前,在 ALTER TABLE mytable DEFAULT CHARACTER SET utf8;
和 C3A96CC3A96D656E7473
(utf8) 之后仍然是 E96CE96D656E7473
(latin1) ALTER TABLE mytable MODIFY COL2 LONGTEXT CHARACTER SET utf8;
我已经编辑了主帖,总结了目前的情况,并提出了剩下的问题
@D3nsk - 重要的是要检查编码(E9 与 C3A9)是否与 列 的字符集(latin1 与 utf8/utf8mb4)一致。我感觉到它们不同步了,但您的评论暗示它们不是。
@D3nsk - 您能否构建一个包含所有创建表、集合、选择十六进制、更改等的 1 行表来演示问题?这将使我更容易检验理论。而且,假设某处潜伏着一个真正的错误,它将为提交错误报告提供证据。
编码似乎与列一致。当我执行以下操作时,它们不同步:set NAMES latin1;
然后INSERT INTO ... "éléments"...
然后ALTER TABLE mytable MODIFY COL2 LONGTEXT CHARACTER SET utf8;
。但在我最初的用例中,连接编码被声明为 utf8 而不是 latin1(抱歉,我在上一篇文章中让事情变得混乱了)。以上是关于Alter table default character set 修改 MySQL 5.6 中的行的主要内容,如果未能解决你的问题,请参考以下文章
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