(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
select rand()*3;
+------------------+
| rand()*3 |
+------------------+
| 2.98752005862772 |
+------------------+
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 ) //符号函数,根据数值返回1(正数) 0(零) -1(负数).
select sign(1);
+---------+
| sign(1) |
+---------+
| 1 |
+---------+
select sign(0);
+---------+
| sign(0) |
+---------+
| 0 |
+---------+
select sign(-1990);
+-------------+
| sign(-1990) |
+-------------+
| -1 |
+-------------+
(3).日期时间类
ADDTIME (date2 ,time_interval ) //将time_interval加到date2
CONVERT_TZ (datetime2 ,fromTZ ,toTZ ) //转换时区
CURRENT_DATE ( ) //当前日期
CURRENT_TIME ( ) //当前时间
CURRENT_TIMESTAMP ( ) //当前时间戳
DATE (datetime ) //返回datetime的日期部分
DATE_ADD (date2 , INTERVAL d_value d_type ) //在date2中加上日期或时间
DATE_FORMAT (datetime ,FormatCodes ) //使用formatcodes格式显示datetime
DATE_SUB (date2 , INTERVAL d_value d_type ) //在date2上减去一个时间
DATEDIFF (date1 ,date2 ) //两个日期差
DAY (date ) //返回日期的天
DAYNAME (date ) //英文星期
DAYOFWEEK (date ) //星期(1-7) ,1为星期天
DAYOFYEAR (date ) //一年中的第几天
EXTRACT (interval_name FROM date ) //从date中提取日期的指定部分
MAKEDATE (year ,day ) //给出年及年中的第几天,生成日期串
MAKETIME (hour ,minute ,second ) //生成时间串
MONTHNAME (date ) //英文月份名
NOW ( ) //当前时间
SEC_TO_TIME (seconds ) //秒数转成时间
STR_TO_DATE (string ,format ) //字串转成时间,以format格式显示
TIMEDIFF (datetime1 ,datetime2 ) //两个时间差
TIME_TO_SEC (time ) //时间转秒数]
WEEK (date_time [,start_of_week ]) //第几周
YEAR (datetime ) //年份
DAYOFMONTH(datetime) //月的第几天
HOUR(datetime) //小时
LAST_DAY(date) //date的月的最后日期
MICROSECOND(datetime) //微秒
MONTH(datetime) //月
MINUTE(datetime) //分返回符号,正负或0
SQRT(number2) //开平方