MySQL之字符函数

MySql中提供一些函数对我们的开发有很多的帮助，下面就把MysQL提供的一些常用函数整理下，首先是字符处理函数：

1.CONCAT()

用法:字符串链接函数，将字符串字段连结在一块

举例：

select concat('MYSQL','Functioin','Test','asian');

结果：

+-----------------------------------------------+
| concat('MYSQL','Functioin','Test','asian') |
+-----------------------------------------------+
|  MYSQLFunctioinTestLasian                  |
+-----------------------------------------------+

2.CONCAT_WS()

用法举例：使用指定的分隔符将字符链接在一块

举例：

 select CONCAT_WS('****','Mysql','Function','test');

　结果：

+---------------------------------------------+
| CONCAT_WS('****','Mysql','Function','test') |
+---------------------------------------------+
| Mysql****Function****test                   |

　　

3.FORMAT()

用法举例：数字格式化

举例：

 select FORMAT(3434.343434,3);

　结果：

+-----------------------+
| FORMAT(3434.343434,3) |
+-----------------------+
| 3,434.343             |
+-----------------------+

4.LOWER()

用法：转换成小写字符

举例：

 select LOWER('MYSQL');

结果：

+----------------+
| LOWER('MYSQL') |
+----------------+
| mysql          |
+----------------+

5.UPPER（）

用法：和LOWER（）用法相反

6.LEFT()

用法：获取左侧字符

举例：

mysql> select LEFT('MYSQL',1);
+-----------------+
| LEFT('MYSQL',1) |
+-----------------+
| M               |
+-----------------+
1 row in set (0.01 sec)

mysql> select LEFT('MYSQL',5);
+-----------------+
| LEFT('MYSQL',5) |
+-----------------+
| MYSQL           |
+-----------------+
1 row in set (0.00 sec)

mysql> select LEFT('MYSQL',7);
+-----------------+
| LEFT('MYSQL',7) |
+-----------------+
| MYSQL           |
+-----------------+
1 row in set (0.00 sec)

当操作字符长度限制的时候会返回真个字符串，但是必须要有数字参数否则会报错

6.RIGHT()

用法：用法和LEFT()类似

mysql> select RIGHT('MYSQL',7);
+------------------+
| RIGHT('MYSQL',7) |
+------------------+
| MYSQL            |
+------------------+
1 row in set (0.00 sec)

mysql> select RIGHT('MYSQL',5);
+------------------+
| RIGHT('MYSQL',5) |
+------------------+
| MYSQL            |
+------------------+
1 row in set (0.00 sec)

mysql> select RIGHT('MYSQL',2);
+------------------+
| RIGHT('MYSQL',2) |
+------------------+
| QL               |
+------------------+
1 row in set (0.00 sec)

7.LENGTH()

用法：获取字符的长度（包括字符内部的空格长度）

mysql> select LENGTH('MYSQL');
+-----------------+
| LENGTH('MYSQL') |
+-----------------+
|               5 |
+-----------------+
1 row in set (0.00 sec)

mysql> select LENGTH('MY  SQL');
+-------------------+
| LENGTH('MY  SQL') |
+-------------------+
|                 7 |
+-------------------+
1 row in set (0.00 sec)

mysql> select LENGTH(' MY  SQL ');
+---------------------+
| LENGTH(' MY  SQL ') |
+---------------------+
|                   9 |
+---------------------+
1 row in set (0.00 sec)

8.TRIM()

用法：删除前导和后导的字符

mysql> select TRIM(' MYSQL ')
    -> ;
+-----------------+
| TRIM(' MYSQL ') |
+-----------------+
| MYSQL           |
+-----------------+
1 row in set (0.00 sec)

mysql> select LENGTH(TRIM(' MYSQL '));
+-------------------------+
| LENGTH(TRIM(' MYSQL ')) |
+-------------------------+
|                       5 |
+-------------------------+
1 row in set (0.00 sec)

mysql> select LENGTH(' MYSQL ');
+-------------------+
| LENGTH(' MYSQL ') |
+-------------------+
|                 7 |
+-------------------+
1 row in set (0.00 sec)

9.LTRIM(),RTRIM()

这两个函数分别是删除前导空格和后导空格

10.SUBSTRING()

用法：截取字符的子串，第一个参数是操作的字符串，第二个是返回子串开始的位置，第三个是返回子串的数目，默认是返回全部，如果

超过长度则返回全部剩余的子串

举例：

mysql> select SUBSTRING('MYSQL',2);
+----------------------+
| SUBSTRING('MYSQL',2) |
+----------------------+
| YSQL                 |
+----------------------+
1 row in set (0.00 sec)

mysql> select SUBSTRING('MYSQL',2,2);
+------------------------+
| SUBSTRING('MYSQL',2,2) |
+------------------------+
| YS                     |
+------------------------+
1 row in set (0.00 sec)

mysql> select SUBSTRING('MYSQL',2,4);
+------------------------+
| SUBSTRING('MYSQL',2,4) |
+------------------------+
| YSQL                   |
+------------------------+
1 row in set (0.00 sec)

11.REPLACE()

用法：替换字符串函数，第一个参数是操作对象，第二个是待替换的字符串，第三个是替换后字符串

举例：

mysql> select REPLACE('mysql','my','replace');
+---------------------------------+
| REPLACE('mysql','my','replace') |
+---------------------------------+
| replacesql                      |
+---------------------------------+
1 row in set (0.00 sec)

12.ASCII(str)

用法：返回字符的ascii码，如果传的值是字符串，则返回第一个字符的ASCII

举例：

mysql> select ASCII('MYSQL')
+----------------+
| ASCII('MYSQL') |
+----------------+
|             77 |
+----------------+
1 row in set (0.02 sec)

mysql> select ASCII('M');
+------------+
| ASCII('M') |
+------------+
|         77 |
+------------+
1 row in set (0.00 sec)

mysql> select ASCII('');
+-----------+
| ASCII('') |
+-----------+
|         0 |
+-----------+
1 row in set (0.00 sec)