(1).字符串类
首先定义一个字符串变量：set @str="lxl";
CHARSET(str)
//返回字串字符集
select charset(@str);
+---------------+
| charset(@str)
|
+---------------+
|
utf8
|
+---------------+
CONCAT (string [,... ]) //连接字串
select concat(@str,"hello");
+----------------------+
|
concat(@str,"hello") |
+----------------------+
|
abcdefghello |
+----------------------+
INSTR (string ,substring )
//返回substring首次在string中出现的位置,不存在返回0
select instr(@str,‘de‘);
+------------------+
| instr(@str,‘de‘)
|
+------------------+
|
4 |
+------------------+
注：string的下标从1开始，并不是0。
select instr(@str,‘oo‘);
+------------------+
| instr(@str,‘oo‘)
|
+------------------+
|
0 |
+------------------+
LOCATE (substring , string [,start_position ] ) 同INSTR,但可指定开始位置
select locate(‘de‘,@str,2);
+---------------------+
|
locate(‘de‘,@str,2)
|
+---------------------+
|
4 |
+---------------------+
LCASE (string )或者 lower(string),//转换成小写
set @str1="ASDFD";
select lcase(@str1);
+--------------+
| lcase(@str1)
|
+--------------+
| asdfd
|
+--------------+
select lower(@str1);
+--------------+
| lower(@str1)
|
+--------------+
| asdfd
|
+--------------+
UASE (string )或者 uppper(string),//转换成大写
select ucase(@str1);
+--------------+
| ucase(@str1)
|
+--------------+
| ASDFD
|
+--------------+
select upper(@str1);
+--------------+
| upper(@str1)
|
+--------------+
| ASDFD
|
+--------------+
LEFT (string ,length ) //从string2中的左边起取length个字符
set @str1="asdfd";
select left(@str,3);
+--------------+
| left(@str,3)
|
+--------------+
|
abc
|
+--------------+
RIGHT(string,length) //取string最后length个字符
select right(‘adfsfsdf‘,3);
+---------------------+
|
right(‘adfsfsdf‘,3) |
+---------------------+
|
sdf
|
+---------------------+
LENGTH (string ) //string长度
select length(@str);
+--------------+
| length(@str)
|
+--------------+
|
7 |
+--------------+
LOAD_FILE (file_name ) //从文件读取内容
在桌面新建一个test.txt文件，“aaaaaaaaaaaaaaaa你好“
select load_file(@path);
+----------------------+
|
load_file(@path) |
+----------------------+
|
aaaaaaaaaaaaaaaa你好|
+----------------------+
LPAD (string
,length ,pad ) //重复用pad加在string开头,直到字串长度为length
set @str1=‘ASDFD‘;
select lpad(@str1,20,‘xx‘);
+----------------------+
|
lpad(@str1,20,‘xx‘) |
+----------------------+
|
xxxxxxxxxxxxxxxASDFD |
+----------------------+
RPAD (string ,length ,pad) //在str后用pad补充,直到长度为length
select rpad(@str,20,‘xx‘);
+----------------------+
|
rpad(@str,20,‘xx‘) |
+----------------------+
|
abcdefgxxxxxxxxxxxxx |
+----------------------+
LTRIM (string) //去除前端空格
set @str1=" ASDFD";
select ltrim(@str1);
+--------------+
| ltrim(@str1)
|
+--------------+
| ASDFD
|
+--------------+
RTRIM (string ) //去除后端空格
set @str1="asssss ";
select rtrim(@str1);
+--------------+
| rtrim(@str1)
|
+--------------+
| asssss
|
+--------------+
TRIM([[BOTH|LEADING|TRAILING] [padding] FROM]string2) //去除指定位置的指定字符
默认删除前后空格：
select trim(‘ brrr ‘);
+------------------+
|
trim(‘ brrr ‘) |
+------------------+
|
brrr
|
+------------------+
删除指定首字符 如’，‘
select trim(leading ‘,‘ from
‘,,,,dfdfdf,,,,‘);
+-----------------------------------------+
|
trim(leading ‘,‘ from ‘,,,,dfdfdf,,,,‘)
|
+-----------------------------------------+
|
dfdfdf,,,,
|
+-----------------------------------------+
删除指定首尾字符 如’，‘
select trim(trailing ‘,‘ from
‘,,,,sdfdfd,,,,‘);
+------------------------------------------+
|
trim(trailing ‘,‘ from ‘,,,,sdfdfd,,,,‘)
|
+------------------------------------------+
|
,,,,sdfdfd
|
+------------------------------------------+
删除指定首尾字符
select trim(both ‘,‘ from
‘,,,,sdfsdfsdf,,,,‘);
+-----------------------------------------+
|
trim(both ‘,‘ from ‘,,,,sdfsdfsdf,,,,‘)
|
+-----------------------------------------+
|
sdfsdfsdf
|
+-----------------------------------------+
REPEAT (string ,count ) //将string重复count次
select repeat(@str,3);
+-----------------------+
|
repeat(@str,3)
|
+-----------------------+
| abcdefgabcdefgabcdefg
|
+-----------------------+
REPLACE (str ,search_str ,replace_str )
//在str中用replace_str替换search_str
select replace(@str,‘abc‘,‘aaa‘);
+---------------------------+
|
replace(@str,‘abc‘,‘aaa‘) |
+---------------------------+
|
aaadefg
|
+---------------------------+
STRCMP (string1 ,string2 ) //逐字符比较两字串大小
set @str="abcdefg";
set @str1="aaaaaaaaaaa";
select strcmp(@str,@str1);
+--------------------+
|
strcmp(@str,@str1)
|
+--------------------+
|
1 |
+--------------------+
set @str1="bbbb";
select strcmp(@str,@str1);
+--------------------+
|
strcmp(@str,@str1)
|
+--------------------+
|
-1 |
+--------------------+
若第一个string大返回1，否则返回-1。
SUBSTRING (str , position [,length ])
//从str的position开始,取length个字符
set @str="abcdefg";
select substring(@str,2,3);
+---------------------+
|
substring(@str,2,3) |
+---------------------+
|
bcd
|
+---------------------+
SPACE(count) //生成count个空格
select concat(space(5),‘aaaa‘);
+-------------------------+
|
concat(space(5),‘aaaa‘)
|
+-------------------------+
|
aaaa
|
+-------------------------+
(2).数学类
ABS
(number2 ) //绝对值
select abs(-3);
+---------+
| abs(-3)
|
+---------+
| 3
|
+---------+
BIN (decimal_number ) //十进制转二进制
select bin(8);
+--------+
| bin(8) |
+--------+
|
1000 |
+--------+
CEILING (number2 ) //向上取整
select ceiling(3.2);
+--------------+
| ceiling(3.2)
|
+--------------+
|
4 |
+--------------+
FLOOR (number2 ) //向下取整
select floor(4.999);
+--------------+
| floor(4.999)
|
+--------------+
|
4 |
+--------------+
CONV(number2,from_base,to_base) //进制转换
select conv(8,10,2);
+--------------+
| conv(8,10,2)
|
+--------------+
| 1000
|
+--------------+
select conv(17,10,16);
+----------------+
| conv(17,10,16)
|
+----------------+
|
11
|
+----------------+
FORMAT (number,decimal_places ) //保留小数位数,会四舍五入
select format(4.12367823,3);
+----------------------+
|
format(4.12367823,3) |
+----------------------+
|
4.124
|
+----------------------+
HEX (DecimalNumber ) //转十六进制
select hex(18);
+---------+
| hex(18) |
+---------+
|
12 |
+---------+
select hex(‘你好吗‘);
+--------------------+
|
hex(‘你好吗‘) |
+--------------------+
|
E4BDA0E5A5BDE59097
|
+--------------------+
：HEX()中可传入字符串，则返回其ASC-11码，如HEX(‘DEF‘)返回4142143
也可以传入十进制整数，返回其十六进制编码，如HEX(25)返回19
LEAST (number , number2 [,..]) //求最小值
select least(2,4,6,3,8,5);
+--------------------+
|
least(2,4,6,3,8,5)
|
+--------------------+
|
2 |
+--------------------+
MOD (numerator ,denominator ) //求余
select mod(10,3);
+-----------+
| mod(10,3)
|
+-----------+
| 1
|
+-----------+
POWER (number ,power ) //求指数
select power(2,3);
+------------+
| power(2,3)
|
+------------+
| 8
|
+------------+
RAND([seed]) //随机数
ROUND (number [,decimals ])
//四舍五入,decimals为小数位数]
注：返回类型并非均为整数，如：
(1)默认变为整形值
mysql> select round(1.23);
+-------------+
| round(1.23) |
+-------------+
| 1 |
+-------------+
1 row in set
(0.00 sec)
mysql>
select round(1.56);
+-------------+
| round(1.56) |
+-------------+
| 2 |
+-------------+
1 row in set
(0.00 sec)
(2)可以设定小数位数，返回浮点型数据
mysql> select round(1.567,2);
+----------------+
| round(1.567,2) |
+----------------+
| 1.57 |
+----------------+
1 row in
set (0.00 sec)
SIGN (number2 ) //