mysql中utf8 ,utf8mb4区别转化方法

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mysql中utf8 ,utf8mb4区别转化方法

派大星110 2018-12-03 20:06:37 浏览4831
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mysql中的utf8

mysql中的“utf8”最大只支持3 个bytes,而真正的utf8编码(大家都使用的标准),最大支持4个bytes。正是由于mysql的utf8少一个byte,导致中文的一些特殊字符和emoji都无法正常的显示。mysql真正的utf8其实是utf8mb4,这是在5.5版本之后加入的。而目前的“utf8”其实是utf8mb3。mb就是 max bytes的意思(猜测)。所以尽量不要使用默认的utf8,使用utf8mb4才是正确的选择。

mysql> show create table t1;
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                        |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t1    | CREATE TABLE `t1` (
  `info` varchar(10) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>
mysql>
mysql>
mysql>
mysql>
mysql>
mysql> select length('你');
+---------------+
| length('你')  |
+---------------+
|             3 |
+---------------+
1 row in set (0.00 sec)

mysql> select length('𩱻');
+-------------+
| length('?') |
+-------------+
|           4 |
+-------------+
1 row in set (0.00 sec)

mysql>
mysql>
mysql> insert into t1 value('你');
Query OK, 1 row affected (0.05 sec)

mysql> insert into t1 value('𩱻');
ERROR 1366 (HY000): Incorrect string value: '\xF0\xA9\xB1\xBB' for column 'info' at row 1
mysql>

创建了一个编码为utf8的列info,插入byte长度分别为3位和4位的中文,可以发现插入4位中文是报错。同样我们看看emoji表情:
_2018_12_04_12_08_28

utf8可以直接转成utf8mb4,使用ALTER TABLE ... CONVERT TO CHARACTER SET ...语句,这是由于utf8是utf8mb4的子集。其他类型最好不要直接转,会出现问题,比如latin转utf8.
这篇文章描述了一种错误情况。

查看数据库支持的编码

> mysql> select * from information_schema.CHARACTER_SETS;  
> +--------------------+----------------------+---------------------------------+--------+  
> | CHARACTER_SET_NAME | DEFAULT_COLLATE_NAME | DESCRIPTION                     | MAXLEN |  
> +--------------------+----------------------+---------------------------------+--------+  
> | big5               | big5_chinese_ci      | Big5 Traditional Chinese        |      2 |  
> | dec8               | dec8_swedish_ci      | DEC West European               |      1 |  
> | cp850              | cp850_general_ci     | DOS West European               |      1 |  
> | hp8                | hp8_english_ci       | HP West European                |      1 |  
> | koi8r              | koi8r_general_ci     | KOI8-R Relcom Russian           |      1 |  
> | latin1             | latin1_swedish_ci    | cp1252 West European            |      1 |  
> | latin2             | latin2_general_ci    | ISO 8859-2 Central European     |      1 |  
> | swe7               | swe7_swedish_ci      | 7bit Swedish                    |      1 |  
> | ascii              | ascii_general_ci     | US ASCII                        |      1 |  
> | ujis               | ujis_japanese_ci     | EUC-JP Japanese                 |      3 |  
> | sjis               | sjis_japanese_ci     | Shift-JIS Japanese              |      2 |  
> | hebrew             | hebrew_general_ci    | ISO 8859-8 Hebrew               |      1 |  
> | tis620             | tis620_thai_ci       | TIS620 Thai                     |      1 |  
> | euckr              | euckr_korean_ci      | EUC-KR Korean                   |      2 |  
> | koi8u              | koi8u_general_ci     | KOI8-U Ukrainian                |      1 |  
> | gb2312             | gb2312_chinese_ci    | GB2312 Simplified Chinese       |      2 |  
> | greek              | greek_general_ci     | ISO 8859-7 Greek                |      1 |  
> | cp1250             | cp1250_general_ci    | Windows Central European        |      1 |  
> | gbk                | gbk_chinese_ci       | GBK Simplified Chinese          |      2 |  
> | latin5             | latin5_turkish_ci    | ISO 8859-9 Turkish              |      1 |  
> | armscii8           | armscii8_general_ci  | ARMSCII-8 Armenian              |      1 |  
> | utf8               | utf8_general_ci      | UTF-8 Unicode                   |      3 |  
> | ucs2               | ucs2_general_ci      | UCS-2 Unicode                   |      2 |  
> | cp866              | cp866_general_ci     | DOS Russian                     |      1 |  
> | keybcs2            | keybcs2_general_ci   | DOS Kamenicky Czech-Slovak      |      1 |  
> | macce              | macce_general_ci     | Mac Central European            |      1 |  
> | macroman           | macroman_general_ci  | Mac West European               |      1 |  
> | cp852              | cp852_general_ci     | DOS Central European            |      1 |  
> | latin7             | latin7_general_ci    | ISO 8859-13 Baltic              |      1 |  
> | cp1251             | cp1251_general_ci    | Windows Cyrillic                |      1 |  
> | utf16              | utf16_general_ci     | UTF-16 Unicode                  |      4 |  
> | utf16le            | utf16le_general_ci   | UTF-16LE Unicode                |      4 |  
> | cp1256             | cp1256_general_ci    | Windows Arabic                  |      1 |  
> | cp1257             | cp1257_general_ci    | Windows Baltic                  |      1 |  
> | utf32              | utf32_general_ci     | UTF-32 Unicode                  |      4 |  
> | binary             | binary               | Binary pseudo charset           |      1 |  
> | geostd8            | geostd8_general_ci   | GEOSTD8 Georgian                |      1 |  
> | cp932              | cp932_japanese_ci    | SJIS for Windows Japanese       |      2 |  
> | eucjpms            | eucjpms_japanese_ci  | UJIS for Windows Japanese       |      3 |  
> | gb18030            | gb18030_chinese_ci   | China National Standard GB18030 |      4 |  
> | utf8mb4            | utf8mb4_0900_ai_ci   | UTF-8 Unicode                   |      4 |  
> +--------------------+----------------------+---------------------------------+--------+

由于mysql中utf8的maxlen是3个byte,而正常的unicode使用的是2~4个byte,导致mysql的 不能显示emoji和一些生僻的中文。所以mysql又推出了uft8mb4,这个才是真正的utf8编码。不过在oracle接手mysql之后,默认的字符编码之后会改成utf8mb4。这里详细阐述了mysql utf8编码的坑以及应对方法。

服务器参数设置

[mysqld]
character_set_server=utf8mb4

aws云上数据库设置

参数组中:

  • character_set_client
  • character_set_connection
  • character_set_database
  • character_set_results
  • character_set_server
    这几个参数设置成utf8mb4,不过这里有个限制,aws的数据传输工具DMS中不支持utf8mb4编码,有这类需求的同学需要注意。--已经在3.1.1版本中修复。

官方文档:dms限制

查询当前字符集设置

查看参数

mysql> show variables like 'character%';
+--------------------------+------------------------------------------------------+
| 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                                                 |
| character_sets_dir       | /usr/local/Cellar/mysql/8.0.12/share/mysql/charsets/ |
+--------------------------+------------------------------------------------------+

查看数据库字符集

mysql> select * from information_schema.SCHEMATA;
+--------------+--------------------+----------------------------+------------------------+----------+
| CATALOG_NAME | SCHEMA_NAME        | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH |
+--------------+--------------------+----------------------------+------------------------+----------+
| def          | mysql              | utf8                       | utf8_general_ci        |     NULL |
| def          | information_schema | utf8                       | utf8_general_ci        |     NULL |
| def          | performance_schema | utf8mb4                    | utf8mb4_0900_ai_ci     |     NULL |
| def          | sys                | utf8mb4                    | utf8mb4_0900_ai_ci     |     NULL |
| def          | mydb               | utf8mb4                    | utf8mb4_unicode_ci     |     NULL |
| def          | t1                 | utf8mb4                    | utf8mb4_0900_ai_ci     |     NULL |
+--------------+--------------------+----------------------------+------------------------+----------+

查看表的字符集

mysql> show create table t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `description` varchar(50) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
mysql> show table status from t1\G
*************************** 1. row ***************************
           Name: t3
         Engine: InnoDB
        Version: 10
     Row_format: Dynamic
           Rows: 0
 Avg_row_length: 0
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 0
 Auto_increment: NULL
    Create_time: 2018-11-28 12:05:37
    Update_time: NULL
     Check_time: NULL
      Collation: utf8mb4_0900_ai_ci
       Checksum: NULL
 Create_options:
        Comment:
1 row in set (0.15 sec)

这种情况只能看到Collation,Collation的概念是字符比较的规则,每种字符集都会有其默认的Collation,我们从information_schema.CHARACTER_SETS这个表中可以查询到相应的信息,一般我们设定好字符集之后,Collation会被默认该字符集的默认值。

查看所有表的字符集

mysql> select TABLE_SCHEMA,TABLE_NAME,TABLE_COLLATION from information_schema.tables where table_schema = 'mydb';
+--------------+---------------------+--------------------+
| TABLE_SCHEMA | TABLE_NAME          | TABLE_COLLATION    |
+--------------+---------------------+--------------------+
| mydb         | charset_test_latin1 | utf8mb4_0900_ai_ci |
| mydb         | student             | utf8_general_ci    |
| mydb         | t1                  | utf8mb4_0900_ai_ci |
| mydb         | t2                  | utf8_general_ci    |
| mydb         | t3                  | utf8_general_ci    |
| mydb         | t4                  | utf8_general_ci    |
| mydb         | t5                  | utf8mb4_unicode_ci |
| mydb         | t6                  | utf8mb4_0900_ai_ci |
| mydb         | t8                  | utf8mb4_unicode_ci |
| mydb         | vc                  | utf8mb4_unicode_ci |
+--------------+---------------------+--------------------+

这种方法可以查看到一个数据库中所有表的TABLE_COLLATION,推导出对应使用什么类型的字符集。

查看所有列的字符集

mysql> select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,DATA_TYPE,CHARACTER_SET_NAME,COLLATION_NAME from information_schema.columns where TABLE_SCHEMA='mydb';
+--------------+---------------------+-------------+-----------+--------------------+--------------------+
| TABLE_SCHEMA | TABLE_NAME          | COLUMN_NAME | DATA_TYPE | CHARACTER_SET_NAME | COLLATION_NAME     |
+--------------+---------------------+-------------+-----------+--------------------+--------------------+
| mydb         | charset_test_latin1 | id          | int       | NULL               | NULL               |
| mydb         | charset_test_latin1 | char_col    | varchar   | utf8mb4            | utf8mb4_0900_ai_ci |
| mydb         | student             | course      | varchar   | utf8               | utf8_general_ci    |
| mydb         | student             | mark        | int       | NULL               | NULL               |
| mydb         | student             | name        | varchar   | utf8               | utf8_general_ci    |
| mydb         | t1                  | id          | int       | NULL               | NULL               |
| mydb         | t1                  | description | varchar   | utf8mb4            | utf8mb4_0900_ai_ci |
| mydb         | t2                  | info        | varchar   | utf8               | utf8_general_ci    |
| mydb         | t3                  | info        | varchar   | utf8mb4            | utf8mb4_0900_ai_ci |
| mydb         | t4                  | info        | char      | utf8mb4            | utf8mb4_0900_ai_ci |
| mydb         | t5                  | info        | char      | utf8mb4            | utf8mb4_unicode_ci |
| mydb         | t6                  | info        | varchar   | utf8mb4            | utf8mb4_0900_ai_ci |
| mydb         | t8                  | id          | int       | NULL               | NULL               |
| mydb         | vc                  | v           | varchar   | utf8mb4            | utf8mb4_unicode_ci |
| mydb         | vc                  | c           | char      | utf8mb4            | utf8mb4_unicode_ci |
+--------------+---------------------+-------------+-----------+--------------------+--------------------+

utf8 转 utf8mb4

For each database:

ALTER DATABASE
    database_name
    CHARACTER SET = utf8mb4
    COLLATE = utf8mb4_unicode_ci;

For each table:

ALTER TABLE
    table_name
    CONVERT TO CHARACTER SET utf8mb4
    COLLATE utf8mb4_unicode_ci;

For each column:

ALTER TABLE
    table_name
    CHANGE column_name column_name
    data_type
    CHARACTER SET utf8mb4
    COLLATE utf8mb4_unicode_ci;

utf8是utf8mb4的子集,所以直接转换理论上不会有问题。当然也可以使用dump转换编码。
批量生成脚本:

use information_schema;
SELECT concat("ALTER DATABASE `",table_schema,"` CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;") as _sql 
FROM `TABLES` where table_schema like "yourDbName" group by table_schema;

SELECT concat("ALTER TABLE `",table_schema,"`.`",table_name,"` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;") as _sql  
FROM `TABLES` where table_schema like "yourDbName" group by table_schema, table_name;

SELECT concat("ALTER TABLE `",table_schema,"`.`",table_name, "` CHANGE `",column_name,"` `",column_name,"` ",data_type,"(",character_maximum_length,") CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;") as _sql 
FROM `COLUMNS` where table_schema like "yourDbName" and data_type in ('varchar');

SELECT concat("ALTER TABLE `",table_schema,"`.`",table_name, "` CHANGE `",column_name,"` `",column_name,"` ",data_type," CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;") as _sql 
FROM `COLUMNS` where table_schema like "yourDbName" and data_type in ('text','tinytext','mediumtext','longtext');

ERROR 1071 (42000) 问题解决

出现这种报错主要有两种情况:

ERROR 1071 (42000): Specified key was too long; max key length is 3072 bytes
ERROR 1071 (42000): Specified key was too long; max key length is 1000 bytes

一个是length 大于3072 bytes,一个是大于1000 bytes。

mysql5.7中支持index key最大的长度是 767 bytes,在开启了innodb_large_prefix这个参数之后,max len 限制是3072 bytes。在5.7之前这个参数没有默认开启,5.7之后默认是开启的。8.0之后去掉了这个参数,默认就支持3072个字节。

所以在转换字符集过程中,如果一个列上有索引,由于之前的utf8的编码是3个bytes,utf8mb4是4个bytes。转换之后key的值可能会超过767或则3072,这个时候就是出现类似的报错。如果是MyISAM的引擎,是直接不能超过1000 bytes这个限制的。

这个时候的解决办法是如果是MyISAM的引擎,改成innodb引擎。

如果改成innodb还不行,只能缩小字段的大小。

常用命令

set names utf8mb4;
相当于设置

  • character_set_client
  • character_set_connection
  • character_set_results
    三个值为utf8mb4.

总结

不得不说,mysql这个3个byte的utf8是个巨坑,没有按照国际的标准来设计,不过之后肯定会改成utf8mb4为默认字符集。

参考连接

https://dba.stackexchange.com/questions/8239/how-to-easily-convert-utf8-tables-to-utf8mb4-in-mysql-5-5

http://aprogrammers.blogspot.com/2014/12/utf8mb4-character-set-in-amazon-rds.html

https://oracle-base.com/articles/mysql/mysql-converting-table-character-sets-from-latin1-to-utf8#the-problem

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