MySQL中常见字符串操作函数

字符串连接 concat

mysql> select concat ('who',' ','am',' ','I?')
-> ;
+----------------------------------+
| concat ('who',' ','am',' ','I?') |
+----------------------------------+
| who am I?                        |
+----------------------------------+
1 row in set (0.00 sec)

ORACLE中用 || ，sql server 中用+

长度函数 length

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

定位函数 position、locate

position

mysql> select position('3' in '0123');
+-------------------------+
| position('3' in '0123') |
+-------------------------+
|                       4 |
+-------------------------+
1 row in set (0.00 sec)

locate

mysql> select locate('3' ,'0123',3);
+-----------------------+
| locate('3' ,'0123',3) |
+-----------------------+
|                     4 |
+-----------------------+
1 row in set (0.00 sec)

mysql> select locate('3' ,'0123',4);
+-----------------------+
| locate('3' ,'0123',4) |
+-----------------------+
|                     4 |
+-----------------------+
1 row in set (0.00 sec)

mysql> select locate('3' ,'0123',5);
+-----------------------+
| locate('3' ,'0123',5) |
+-----------------------+
|                     0 |
+-----------------------+
1 row in set (0.00 sec)

oracle用instr()和locat()来实现上面两个功能，sql server 用charindex()来实现

case功能：strcmp(),regexp,like

类似oracle中的case功能，MySQL中有以下函数

strcmp()

select strcmp(‘123’,’abc’)

比较两个字符串的次序：

前者排序在后者之前返回-1

两个字符串相同返回0

后者排序在前者之前返回1

like

如果like命中则返回1，不命中返回0

mysql> select a like '%bb' from (select 'abb' a) a
-> ;
+--------------+
| a like '%bb' |
+--------------+
|            1 |
+--------------+
1 row in set (0.01 sec)

mysql> select a like '%bb' from (select 'abbc' a) a;
+--------------+
| a like '%bb' |
+--------------+
|            0 |
+--------------+
1 row in set (0.00 sec)

regexp

格式化函数，如果是预期格式返回1，不是是0

mysql> select a regexp '.{a}-.{a}-.{a}-.{a}' from (select 'a-b-b-c' a) a;
+--------------------------------+
| a regexp '.{a}-.{a}-.{a}-.{a}' |
+--------------------------------+
|                              0 |
+--------------------------------+
1 row in set (0.01 sec)

mysql> select a regexp '.{1}-.{1}-.{1}-.{1}' from (select 'a-b-b-c' a) a;
+--------------------------------+
| a regexp '.{1}-.{1}-.{1}-.{1}' |
+--------------------------------+
|                              1 |
+--------------------------------+
1 row in set (0.00 sec)

ascii 函数

这个函数用来看单个字符的排序数字

mysql> select ascii('1');
+------------+
| ascii('1') |
+------------+
|         49 |
+------------+
1 row in set (0.00 sec)

mysql> select ascii('2');
+------------+
| ascii('2') |
+------------+
|         50 |
+------------+
1 row in set (0.00 sec)

mysql> select ascii('a');
+------------+
| ascii('a') |
+------------+
|         97 |
+------------+
1 row in set (0.00 sec)

mysql> select ascii('A');
+------------+
| ascii('A') |
+------------+
|         65 |
+------------+
1 row in set (0.00 sec)

insert 函数

有4个参数，分别表示：原始字符串、字符串操作开始位置、要替换字符串的个数、插入字符串

mysql> select insert('adef',2,0,'bc') string;
+--------+
| string |
+--------+
| abcdef |
+--------+
1 row in set (0.00 sec)

mysql> select insert('adef',2,1,'bc') string;
+--------+
| string |
+--------+
| abcef  |
+--------+
1 row in set (0.00 sec)

mysql> select insert('adef',2,2,'bc') string;
+--------+
| string |
+--------+
| abcf   |
+--------+
1 row in set (0.00 sec)

oracle用replace函数，sql server 用replace和stuff函数。

substring() 字符串截取函数

这个函数应该比较常见，oracle中用substr()，sql server总用的也是substring

mysql> select substring('abcd123efg',5,3);
+-----------------------------+
| substring('abcd123efg',5,3) |
+-----------------------------+
| 123                         |
+-----------------------------+
1 row in set (0.00 sec)

上面例子把字符串abcd123efg中的123提取出来，第一个参数为原始字符串，第2个参数为从哪个位置开始提取，第3个参数为提取多长的字符串。