mysql-函数:字符串函数

select concat('a','b','cde','fff'); -- 字符串连接

+-----------------------------+
| concat('a','b','cde','fff') |
+-----------------------------+
| abcdefff                    |
+-----------------------------+
1 row in set (0.00 sec)

select concat_ws(';','abc','def','ggg'); --  使用分隔符连接字符串

+----------------------------------+
| concat_ws(';','abc','def','ggg') |
+----------------------------------+
| abc;def;ggg                      |
+----------------------------------+
1 row in set (0.00 sec)

select instr('iloveyoukate','you'); -- 返回第一个子串的位置，从1开始

+-----------------------------+
| instr('iloveyoukate','you') |
+-----------------------------+
|                           6 |
+-----------------------------+
1 row in set (0.00 sec)

select insert('abcdefghijkl',2,10,'---'); --  从第二个位置开始替换10个字符

root@localhost:stu>select insert('abcdefghijkl',2,10,'---');
+-----------------------------------+
| insert('abcdefghijkl',2,10,'---') |
+-----------------------------------+
| a---l                             |
+-----------------------------------+
1 row in set (0.00 sec)

select lower('CatIsPet'); --  变小写

root@localhost:stu>select lower('CatIsPet');
+-------------------+
| lower('CatIsPet') |
+-------------------+
| catispet          |
+-------------------+
1 row in set (0.00 sec)

select upper('CatIsPet'); --  变大写

root@localhost:stu>select upper('CatIsPet');
+-------------------+
| upper('CatIsPet') |
+-------------------+
| CATISPET          |
+-------------------+
1 row in set (0.02 sec)

select left('CatIsPet',3); --  取最左边三个字符

root@localhost:stu>select left('CatIsPet',3);
+--------------------+
| left('CatIsPet',3) |
+--------------------+
| Cat                |
+--------------------+
1 row in set (0.00 sec)

select trim('   a  bc  '); -- 去除两端空格

root@localhost:stu>select trim('   a  bc  ');
+--------------------+
| trim('   a  bc  ') |
+--------------------+
| a  bc              |
+--------------------+
1 row in set (0.00 sec)

select substring('DomLikeYou',4); -- 从4位值开始取所有字符

root@localhost:stu>select substring('DomLikeYou',4);
+---------------------------+
| substring('DomLikeYou',4) |
+---------------------------+
| LikeYou                   |
+---------------------------+
1 row in set (0.00 sec)

select substring('DomLikeYou',4,7); -- 从4位置开始取7个字符

root@localhost:stu>select substring('DomLikeYou',4,7);
+-----------------------------+
| substring('DomLikeYou',4,7) |
+-----------------------------+
| LikeYou                     |
+-----------------------------+
1 row in set (0.00 sec)

select repeat('abc',3); -- 重复三遍abc

root@localhost:stu>select repeat('abc',3);
+-----------------+
| repeat('abc',3) |
+-----------------+
| abcabcabc       |
+-----------------+
1 row in set (0.00 sec)

select reverse('Love'); -- 翻转字符串

root@localhost:stu>select reverse('Love');
+-----------------+
| reverse('Love') |
+-----------------+
| evoL            |
+-----------------+
1 row in set (0.00 sec)

select replace('IHateYou','Hate','Love'); -- 替换Hate为Love

root@localhost:stu>select replace('IHateYou','Hate','Love');
+-----------------------------------+
| replace('IHateYou','Hate','Love') |
+-----------------------------------+
| ILoveYou                          |
+-----------------------------------+
1 row in set (0.00 sec)

select left('DogIsPet',3); -- 返回最左边的3个字符

root@localhost:stu>select left('DogIsPet',3);
+--------------------+
| left('DogIsPet',3) |
+--------------------+
| Dog                |
+--------------------+
1 row in set (0.00 sec)

select right('DogIsPet',3); -- 返回最右边3个字符

root@localhost:stu>select right('DogIsPet',3); -- 返回最右边的3个字符
+---------------------+
| right('DogIsPet',3) |
+---------------------+
| Pet                 |
+---------------------+
1 row in set (0.00 sec)