Mysql 字符串函数(1)

1.left(str,length) 字符串截取函数

mysql> select left('string',2);+------------------+| left('string',2) |+------------------+| st               |+------------------+1 row in set (0.00 sec)

2.right(str,length) 字符串截取函数

mysql> select right('string',3);+-------------------+| right('string',3) |+-------------------+| ing               |+-------------------+1 row in set (0.00 sec)

3.substring(str,pos) 字符串截取函数

mysql> select substring('string',2);/*截取左边第二个字符到最后*/+-----------------------+| substring('string',2) |+-----------------------+| tring                |+-----------------------+1 row in set (0.00 sec)mysql> select substring('string',-4);/*从后往前截取4个字符*/+------------------------+| substring('string',-4) |+------------------------+| ring                   |+------------------------+1 row in set (0.00 sec)

4.substring(str,begin_pos,length);字符串截取

mysql> select substring('string',3,2);/*从左边第三个字符开始，截取两个字符*/+-------------------------+| substring('string',3,2) |+-------------------------+| ri                      |+-------------------------+1 row in set (0.00 sec)mysql> select substring('string',-6,2);/*从前向后倒数第6个字符开始向后去2个字符*/+--------------------------+| substring('string',-6,2) |+--------------------------+| st                       |+--------------------------+1 row in set (0.00 sec)

注：substring函数中的第二个参数pos可以为负数，表示从后向前算，但是length不能为负，为负时返回为空串

5.substring_index(str,char,count)

mysql> select substring_index('www.csdn.net','.',2);/*截取从开始到第二个‘.’出的字符串*/+---------------------------------------+| substring_index('www.csdn.net','.',2) |+---------------------------------------+| www.csdn                              |+---------------------------------------+1 row in set (0.00 sec)mysql> select substring_index('www.csdn.net','.',-2);/*截取倒数第二个‘.’到最后的字符串*/+----------------------------------------+| substring_index('www.csdn.net','.',-2) |+----------------------------------------+| csdn.net                               |+----------------------------------------+1 row in set (0.00 sec)mysql> select substring_index('www.csdn.net','a',-2);/*如果所截取字符串中没有所要匹配的字符，则返回整个字符串*/+----------------------------------------+| substring_index('www.csdn.net','a',-2) |+----------------------------------------+| www.csdn.net                           |+----------------------------------------+1 row in set (0.00 sec)