MySQL判斷中文字符的方法（轉）

准備：

2.1、環境

MySQL

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、創建測試表和插入測試數據 

MySQL

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

創建測試表和插入測試數據。

MySQL

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('溫國兵');
Query OK, 1 row affected (0.00 sec)

方法：

3.1、方法一：正則表達式 

MySQL

mysql> SELECT * FROM user G;
*************************** 1. row ***************************
name: robin
*************************** 2. row ***************************
name: 溫國兵
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 "判斷是否是中文字符"
    -> FROM user;
+-----------+-----------------------------+
| name      | 判斷是否是中文字符 |
+-----------+-----------------------------+
| robin     | 不是中文字符          |
| 溫國兵 | 是中文字符             |
+-----------+-----------------------------+
2 rows in set (0.00 sec)
 
mysql> SELECT name FROM user WHERE NOT (name REGEXP "[u0391-uFFE5]");
+-----------+
| name      |
+-----------+
| 溫國兵 |
+-----------+
1 row in set (0.00 sec)

3.2、方法二：length()和char_length() 

MySQL

mysql> SELECT name, length(name), char_length(name) FROM user;
+-----------+--------------+-------------------+
| name      | length(name) | char_length(name) |
+-----------+--------------+-------------------+
| robin     |            5 |                 5 |
| 溫國兵 |           20 |                 9 |
+-----------+--------------+-------------------+
2 rows in set (0.00 sec)
 
mysql> SELECT name FROM user WHERE length(name)  char_length(name);
+-----------+
| name      |
+-----------+
| 溫國兵 |
+-----------+
1 row in set (0.00 sec)

總結

方法一中，[u0391-uFFE5]匹配中文以外的字符。

方法二中，當字符集為UTF-8，並且字符為中文時，length()和char_length()兩個方法返回的結果不相同。

參考官方文檔：

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.

Ref

12.5 String Functions

 

參考：

http://blog.jobbole.com/94567/（以上內容轉自此篇文章）