如何在 MySQL 中判断中文字符？

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一引子

在生产环境中，经常会有这样的场景：获得中文数据。那问题就来了，怎么才能匹配出中文字符呢？

本文提供两种方法。

二演示

2.1 环境

mysql> SHOW VARIABLES LIKE "%version%";
+-------------------------+------------------------------+
| Variable_name | Value |
+-------------------------+------------------------------+
| protocol_version | 10 |
| version | 5.1.73 |
| version_comment | MySQL Community Server (GPL) |
| version_compile_machine | i386 |
| version_compile_os | apple-darwin10.3.0 |
+-------------------------+------------------------------+
5 rows in set (0.00 sec)

2.2 创建测试表和插入测试数据

mysql -S /tmp/mysql_5173.sock -uroot -proot

创建测试表和插入测试数据。

mysql> USE test;
Database changed

mysql> CREATE TABLE user
-> (name VARCHAR(20)
-> ) DEFAULT CHARSET = utf8 ENGINE = INNODB;
Query OK, 0 rows affected (0.10 sec)

mysql> SHOW TABLE STATUS LIKE 'user' \G;
*************************** 1. row ***************************
Name: user
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 2
Avg_row_length: 8192
Data_length: 16384
Max_data_length: 0
Index_length: 0
Data_free: 0
Auto_increment: NULL
Create_time: 2015-01-16 18:01:36
Update_time: NULL
Check_time: NULL
Collation: utf8_general_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)

ERROR:
No query specified

mysql> INSERT INTO user VALUES('robin');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO user VALUES('温国兵');
Query OK, 1 row affected (0.00 sec)

三实现

3.1 方法一正则表达式

mysql> SELECT * FROM user \G;
*************************** 1. row ***************************
name: robin
*************************** 2. row ***************************
name: 温国兵
2 rows in set (0.00 sec)

mysql> SELECT name,
-> CASE name REGEXP "[\u0391-\uFFE5]"
-> WHEN 1 THEN "不是中文字符"
-> ELSE "是中文字符"
-> END AS "判断是否是中文字符"
-> FROM user;
+-----------+-----------------------------+
| name | 判断是否是中文字符 |
+-----------+-----------------------------+
| robin | 不是中文字符 |
| 温国兵 | 是中文字符 |
+-----------+-----------------------------+
2 rows in set (0.00 sec)

mysql> SELECT name FROM user WHERE NOT (name REGEXP "[\u0391-\uFFE5]");
+-----------+
| name |
+-----------+
| 温国兵 |
+-----------+
1 row in set (0.00 sec)

3.2 方法二 length() 和 char_length()

mysql> SELECT name, length(name), char_length(name) FROM user;
+-----------+--------------+-------------------+
| name | length(name) | char_length(name) |
+-----------+--------------+-------------------+
| robin | 5 | 5 |
| 温国兵 | 20 | 9 |
+-----------+--------------+-------------------+
2 rows in set (0.00 sec)

mysql> SELECT name FROM user WHERE length(name) <> char_length(name);
+-----------+
| name |
+-----------+
| 温国兵 |
+-----------+
1 row in set (0.00 sec)

四总结

方法一中，[\u0391-\uFFE5] 匹配中文以外的字符。

方法二中，当字符集为UTF-8，并且字符为中文时，length() 和 char_length() 两个方法返回的结果不相同。

参考官方文档：

LENGTH()
Return the length of a string in bytes
Returns the length of the string str, measured in bytes. A multibyte character counts as multiple bytes. This means that for a string containing five 2-byte characters, LENGTH() returns 10, whereas CHAR_LENGTH() returns 5.

CHAR_LENGTH()
Return number of characters in argument
Returns the length of the string str, measured in characters. A multibyte character counts as a single character. This means that for a string containing five 2-byte characters, LENGTH() returns 10, whereas CHAR_LENGTH() returns 5.

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