MySQL字符函数
CONCAT()和CONCAT_WS()字符连接
mysql> SELECT CONCAT('mysql','5.6');
+-----------------------+
| CONCAT('mysql','5.6') |
+-----------------------+
| mysql5.6 |
+-----------------------+
1 row in set (0.09 sec)
mysql> SELECT CONCAT('mysql','-','5.6');
+---------------------------+
| CONCAT('mysql','-','5.6') |
+---------------------------+
| mysql-5.6 |
+---------------------------+
1 row in set (0.00 sec)
例如：将用户的first_name和last_name连接起来成一个字符串
mysql> SELECT * FROM tdb_test; +----+------------+-----------+ | id | first_name | last_name | +----+------------+-----------+ | 1 | A | B | | 2 | Jack | Bob | | 3 | tom% | 123 | +----+------------+-----------+ 3 rows in set (0.00 sec) mysql> SELECT CONCAT(first_name,last_name) AS fullname FROM tdb_test; +----------+ | fullname | +----------+ | AB | | JackBob | | tom%123 | +----------+ 3 rows in set (0.00 sec)
CONCAT_WS()的第一个参数为分隔符，后面的为要连接的字符
mysql> SELECT CONCAT_WS('|','A','B','C');
+----------------------------+
| CONCAT_WS('|','A','B','C') |
+----------------------------+
| A|B|C |
+----------------------------+
1 row in set (0.00 sec)
mysql> SELECT CONCAT_WS('-','mysql','5.6');
+------------------------------+
| CONCAT_WS('-','mysql','5.6') |
+------------------------------+
| mysql-5.6 |
+------------------------------+
1 row in set (0.00 sec)
FORMAT()数字格式化
mysql> SELECT FORMAT(12560.75,1);
+--------------------+
| FORMAT(12560.75,1) |
+--------------------+
| 12,560.8 |
+--------------------+
1 row in set (0.01 sec)
LOWER()和 UPPER()
mysql> SELECT LOWER('MySql');
+----------------+
| LOWER('MySql') |
+----------------+
| mysql |
+----------------+
1 row in set (0.00 sec)
mysql> SELECT UPPER('MySql');
+----------------+
| UPPER('MySql') |
+----------------+
| MYSQL |
+----------------+
1 row in set (0.00 sec)
LEFT()和RIGHT()
分别有两个参数，第一个为所用的字符串，第二个为取几位
例如获取MySQL的前两位
mysql> SELECT LEFT('MySQL',2);
+-----------------+
| LEFT('MySQL',2) |
+-----------------+
| My |
+-----------------+
1 row in set (0.00 sec)
例如获取MySQL的后两位
mysql> SELECT RIGHT('MySQL',2);
+------------------+
| RIGHT('MySQL',2) |
+------------------+
| QL |
+------------------+
1 row in set (0.00 sec)
LENGTH获取字符串长度
mysql> SELECT LENGTH('MySQL');
+-----------------+
| LENGTH('MySQL') |
+-----------------+
| 5 |
+-----------------+
1 row in set (0.02 sec)
LTRIM,RTRIM,TRIM
比如直接用SELECT TRIM(' mysql ');
将会删除mysql的前和后的空格，LTRIM只删除左侧的空格，RTRIM只删除右侧的空格。
其他用法：利用TRIM()删除左右两侧的特定字符。
例如：
mysql> SELECT TRIM(LEADING '?' FROM '??MySQL???'); +-------------------------------------+ | TRIM(LEADING '?' FROM '??MySQL???') | +-------------------------------------+ | MySQL??? | +-------------------------------------+ 1 row in set (0.02 sec) mysql> SELECT TRIM(TRAILING '?' FROM '??MySQL???'); +--------------------------------------+ | TRIM(TRAILING '?' FROM '??MySQL???') | +--------------------------------------+ | ??MySQL | +--------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT TRIM(BOTH '?' FROM '??MySQL???'); +----------------------------------+ | TRIM(BOTH '?' FROM '??MySQL???') | +----------------------------------+ | MySQL | +----------------------------------+ 1 row in set (0.01 sec)
注：TRIM()只能删除前导和后续的，不能删除字符中间的，比如TRIM('My SQL');这个空格就删不掉。
REPLACE()字符串替换
例如将??My??SQL???中的？替换成空
mysql> SELECT REPLACE('??My??SQL???','?','');
+--------------------------------+
| REPLACE('??My??SQL???','?','') |
+--------------------------------+
| MySQL |
+--------------------------------+
1 row in set (0.00 sec)
SUBSTRING()字符串截取
所含参数，从第几位截，截取几位。
mysql> SELECT SUBSTRING('MySQL',1,2);
+------------------------+
| SUBSTRING('MySQL',1,2) |
+------------------------+
| My |
+------------------------+
1 row in set (0.00 sec)
需要注意的是，和编程语言不同的是，第一位是1，不是0。
如果只有从第几位起，没有截取几个，就会，一直截到最后。
mysql> SELECT SUBSTRING('MySQL',3);
+----------------------+
| SUBSTRING('MySQL',3) |
+----------------------+
| SQL |
+----------------------+
1 row in set (0.00 sec)
位置也可以为负值（倒着数）
mysql> SELECT SUBSTRING('MySQL',-1);
+-----------------------+
| SUBSTRING('MySQL',-1) |
+-----------------------+
| L |
+-----------------------+
1 row in set (0.04 sec)
注，只能是起始位置可以有负值，但是截取长度不能有负值。
LIKE模式匹配（常用于查询中）
mysql> SELECT 'MySQL' LIKE 'M%'; +-------------------+ | 'MySQL' LIKE 'M%' | +-------------------+ | 1 | +-------------------+ 1 row in set (0.00 sec)
%是指任意一位或者多位
mysql> SELECT * FROM tdb_test; +----+------------+-----------+ | id | first_name | last_name | +----+------------+-----------+ | 1 | A | B | | 2 | Jack | Bob | | 3 | tom% | 123 | +----+------------+-----------+ 3 rows in set (0.00 sec)
例如查询，姓名中包含o的用户
mysql> SELECT * FROM tdb_test WHERE first_name LIKE '%o%'; +----+------------+-----------+ | id | first_name | last_name | +----+------------+-----------+ | 3 | tom% | 123 | +----+------------+-----------+ 1 row in set (0.00 sec)
例如查询，姓名中包含%的用户
mysql> SELECT * FROM tdb_test WHERE first_name LIKE '%%%'; +----+------------+-----------+ | id | first_name | last_name | +----+------------+-----------+ | 1 | A | B | | 2 | Jack | Bob | | 3 | tom% | 123 | +----+------------+-----------+ 3 rows in set (0.00 sec)
发现显示的是所有查询结果。因为mysql会认为上述的%都为通配符。正确操作如下
mysql> SELECT * FROM tdb_test WHERE first_name LIKE '%1%%' ESCAPE '1'; +----+------------+-----------+ | id | first_name | last_name | +----+------------+-----------+ | 3 | tom% | 123 | +----+------------+-----------+ 1 row in set (0.00 sec)
注：%：任意个字符.
_:任意一个字符。