Mysql字符串函数 | 易学教程

一使用CHAR_LENGTH函数计算字符串字符个数

mysql> SELECT CHAR_LENGTH('date'), CHAR_LENGTH('egg');
+---------------------+--------------------+
| CHAR_LENGTH('date') | CHAR_LENGTH('egg') |
+---------------------+--------------------+
|                   4 |                  3 |
+---------------------+--------------------+
1 row in set (0.00 sec)

二使用LENGTH函数计算字符串长度

mysql> SELECT LENGTH('date'), LENGTH('egg');
+----------------+---------------+
| LENGTH('date') | LENGTH('egg') |
+----------------+---------------+
|              4 |             3 |
+----------------+---------------+
1 row in set (0.00 sec)

三使用CONCAT函数连接字符串

mysql> SELECT CONCAT('My SQL', '5.6'),CONCAT('My',NULL, 'SQL');
+-------------------------+--------------------------+
| CONCAT('My SQL', '5.6') | CONCAT('My',NULL, 'SQL') |
+-------------------------+--------------------------+
| My SQL5.6               | NULL                     |
+-------------------------+--------------------------+
1 row in set (0.00 sec)

四使用CONCAT_WS函数连接带分隔符的字符串

mysql> SELECT CONCAT_WS('-', '1st','2nd', '3rd'), CONCAT_WS('*', '1st', NULL, '3rd');
+------------------------------------+------------------------------------+
| CONCAT_WS('-', '1st','2nd', '3rd') | CONCAT_WS('*', '1st', NULL, '3rd') |
+------------------------------------+------------------------------------+
| 1st-2nd-3rd                        | 1st*3rd                            |
+------------------------------------+------------------------------------+
1 row in set (0.00 sec)

五使用INSERT函数进行字符串替代操作

SELECT INSERT('Quest', 2, 4, 'What') AS col1,
INSERT('Quest', -1, 4, 'What') AS col2,
INSERT('Quest', 3, 100, 'Wh') AS col3;
+-------+-------+------+
| col1  | col2  | col3 |
+-------+-------+------+
| QWhat | Quest | QuWh |
+-------+-------+------+
1 row in set (0.01 sec)

六使用LOWER函数或者LCASE函数将字符串中所有字母字符转换为小写

mysql> SELECT LOWER('BEAUTIFUL'), LCASE('Well');
+--------------------+---------------+
| LOWER('BEAUTIFUL') | LCASE('Well') |
+--------------------+---------------+
| beautiful          | well          |
+--------------------+---------------+
1 row in set (0.01 sec)

七使用UPPER函数或者UCASE函数将字符串中所有字母字符转换为大写

mysql> SELECT UPPER('black'), UCASE('BLacK');
+----------------+----------------+
| UPPER('black') | UCASE('BLacK') |
+----------------+----------------+
| BLACK          | BLACK          |
+----------------+----------------+
1 row in set (0.00 sec)

八使用LEFT函数返回字符串中左边的字符

mysql> SELECT LEFT('football', 5);
+---------------------+
| LEFT('football', 5) |
+---------------------+
| footb               |
+---------------------+
1 row in set (0.00 sec)

九使用RIGHT函数返回字符串中右边的字符

mysql> SELECT RIGHT('football', 4);
+----------------------+
| RIGHT('football', 4) |
+----------------------+
| ball                 |
+----------------------+
1 row in set (0.00 sec)

十使用LPAD函数对字符串进行填充操作

mysql> SELECT LPAD('hello',4,'??'), LPAD('hello',10,'??');
+----------------------+-----------------------+
| LPAD('hello',4,'??') | LPAD('hello',10,'??') |
+----------------------+-----------------------+
| hell                 | ?????hello            |
+----------------------+-----------------------+
1 row in set (0.00 sec)

十一使用RPAD函数对字符串进行填充操作

mysql> SELECT RPAD('hello',4,'?'), RPAD('hello',10,'?');
+---------------------+----------------------+
| RPAD('hello',4,'?') | RPAD('hello',10,'?') |
+---------------------+----------------------+
| hell                | hello?????           |
+---------------------+----------------------+
1 row in set (0.00 sec)

十二使用LTRIM函数删除字符串左边的空格

mysql> SELECT '(  book  )',CONCAT('(',LTRIM('  book  '),')');
+------------+-----------------------------------+
| (  book  ) | CONCAT('(',LTRIM('  book  '),')') |
+------------+-----------------------------------+
| (  book  ) | (book  )                          |
+------------+-----------------------------------+
1 row in set (0.00 sec)

十三使用RTRIM函数删除字符串右边的空格

mysql> SELECT '(  book  )',CONCAT('(', RTRIM ('  book  '),')');
+------------+-------------------------------------+
| (  book  ) | CONCAT('(', RTRIM ('  book  '),')') |
+------------+-------------------------------------+
| (  book  ) | (  book)                            |
+------------+-------------------------------------+
1 row in set (0.00 sec)

十四使用TRIM函数删除字符串两边的空格

mysql> SELECT '(  book  )',CONCAT('(', TRIM('  book  '),')');
+------------+-----------------------------------+
| (  book  ) | CONCAT('(', TRIM('  book  '),')') |
+------------+-----------------------------------+
| (  book  ) | (book)                            |
+------------+-----------------------------------+
1 row in set (0.00 sec)

十五使用TRIM(s1 FROM s)函数删除字符串中两端指定的字符

mysql> SELECT TRIM('xy' FROM 'xyxboxyokxxyxy') ;
+----------------------------------+
| TRIM('xy' FROM 'xyxboxyokxxyxy') |
+----------------------------------+
| xboxyokx                         |
+----------------------------------+
1 row in set (0.00 sec)

十六使用REPEAT函数重复生成相同的字符串

mysql> SELECT REPEAT('MySQL', 3);
+--------------------+
| REPEAT('MySQL', 3) |
+--------------------+
| MySQLMySQLMySQL    |
+--------------------+
1 row in set (0.00 sec)

十七使用SPACE函数生成由空格组成的字符串

mysql> SELECT CONCAT('(', SPACE(6), ')' );
+-----------------------------+
| CONCAT('(', SPACE(6), ')' ) |
+-----------------------------+
| (      )                    |
+-----------------------------+
1 row in set (0.00 sec)

十八使用REPLACE函数进行字符串替代操作

mysql> SELECT REPLACE('xxx.mysql.com', 'x', 'w');
+------------------------------------+
| REPLACE('xxx.mysql.com', 'x', 'w') |
+------------------------------------+
| www.mysql.com                      |
+------------------------------------+
1 row in set (0.00 sec)

十九使用STRCMP函数比较字符串大小

mysql> SELECT STRCMP('txt', 'txt2'),STRCMP('txt2', 'txt'), STRCMP('txt', 'txt');
+-----------------------+-----------------------+----------------------+
| STRCMP('txt', 'txt2') | STRCMP('txt2', 'txt') | STRCMP('txt', 'txt') |
+-----------------------+-----------------------+----------------------+
|                    -1 |                     1 |                    0 |
+-----------------------+-----------------------+----------------------+
1 row in set (0.00 sec)

二十使用SUBSTRING函数获取指定位置处的子字符串

SELECT SUBSTRING('breakfast',5) AS col1,
SUBSTRING('breakfast',5,3) AS col2,
SUBSTRING('lunch', -3) AS col3,
SUBSTRING('lunch', -5, 3) AS col4;
+-------+------+------+------+
| col1  | col2 | col3 | col4 |
+-------+------+------+------+
| kfast | kfa  | nch  | lun  |
+-------+------+------+------+
1 row in set (0.00 sec)

二一使用MID()函数获取指定位置处的子字符串

SELECT MID('breakfast',5) as col1,
MID('breakfast',5,3) as col2,
MID('lunch', -3) as col3,
MID('lunch', -5, 3) as col4;
+-------+------+------+------+
| col1  | col2 | col3 | col4 |
+-------+------+------+------+
| kfast | kfa  | nch  | lun  |
+-------+------+------+------+
1 row in set (0.00 sec)

二二使用LOCATE，POSITION，INSTR函数查找字符串中指定子字符串的开始位置

mysql> SELECT LOCATE('ball','football'),POSITION('ball'IN 'football'),INSTR ('football', 'ball');
+---------------------------+-------------------------------+----------------------------+
| LOCATE('ball','football') | POSITION('ball'IN 'football') | INSTR ('football', 'ball') |
+---------------------------+-------------------------------+----------------------------+
|                         5 |                             5 |                          5 |
+---------------------------+-------------------------------+----------------------------+

二三使用REVERSE函数反转字符串

mysql> SELECT REVERSE('abc');
+----------------+
| REVERSE('abc') |
+----------------+
| cba            |
+----------------+
1 row in set (0.00 sec)

二四使用ELT函数返回指定位置字符串

mysql> SELECT ELT(3,'1st','2nd','3rd'), ELT(3,'net','os');
+--------------------------+-------------------+
| ELT(3,'1st','2nd','3rd') | ELT(3,'net','os') |
+--------------------------+-------------------+
| 3rd                      | NULL              |
+--------------------------+-------------------+
1 row in set (0.00 sec)

二五使用FIELD函数返回指定字符串第一次出现的位置

mysql> SELECT FIELD('Hi', 'hihi', 'Hey', 'Hi', 'bas') as col1,FIELD('Hi', 'Hey', 'Lo', 'Hilo',  'foo') as col2;
+------+------+
| col1 | col2 |
+------+------+
|    3 |    0 |
+------+------+
1 row in set (0.00 sec)

二六使用FIND_IN_SET()函数返回子字符串在字符串列表中的位置

mysql> SELECT FIND_IN_SET('Hi','hihi,Hey,Hi,bas');
+-------------------------------------+
| FIND_IN_SET('Hi','hihi,Hey,Hi,bas') |
+-------------------------------------+
|                                   3 |
+-------------------------------------+
1 row in set (0.00 sec)

二七使用MAKE_SET根据二进制位选取指定字符串

SELECT  MAKE_SET(1,'a','b','c') as col1,
     MAKE_SET(1 | 4,'hello','nice','world') as col2,
     MAKE_SET(1 | 4,'hello','nice',NULL,'world') as col3,
     MAKE_SET(0,'a','b','c') as col4;
+------+-------------+-------+------+
| col1 | col2        | col3  | col4 |
+------+-------------+-------+------+
| a    | hello,world | hello |      |
+------+-------------+-------+------+
1 row in set (0.00 sec)

来源：CSDN

作者：cakincqm

链接：https://blog.csdn.net/chengqiuming/article/details/103834691

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