MySQL的基本函数
charset(str) //返回字串字符集
mysql> select charset('demacia'); +--------------------+ | charset('demacia') | +--------------------+ | utf8 | +--------------------+ 1 row in set
concat(string2 [,... ]) //连接字串
mysql> select concat('陷阵之志','有死无生'); +-------------------------+ | concat('陷阵之志','有死无生') | +-------------------------+ | 陷阵之志有死无生 | +-------------------------+ 1 row in set
lcase(string2 ) //转换成小写
mysql> select lcase('DEMACIA'); +------------------+ | lcase('DEMACIA') | +------------------+ | demacia | +------------------+ 1 row in set
left(string2 ,length ) //从string2中的左边起取length个字符
mysql> select left('demacia',3); +-------------------+ | left('demacia',3) | +-------------------+ | dem | +-------------------+ 1 row in set
length(string ) //string长度
+-------------------+ | length('demacia') | +-------------------+ | 7 | +-------------------+ 1 row in set
load_file(file_name ) //从文件读取内容
instr (string ,substring ) //返回substring首次在string中出现的位置,不存在返回0
mysql> select instr('demacia','a'); +----------------------+ | instr('demacia','a') | +----------------------+ | 4 | +----------------------+ 1 row in set
locate(substring , string [,start_position ] ) 同INSTR,但可指定开始位置
mysql> select locate('demacia',1,4); +-----------------------+ | locate('demacia',1,4) | +-----------------------+ | 0 | +-----------------------+ 1 row in set
substring(str , position [,length ]) //从str的position开始,取length个字符,
mysql> select substring('demacia',1,3); +--------------------------+ | substring('demacia',1,3) | +--------------------------+ | dem | +--------------------------+ 1 row in set
lpad(string2 ,length ,pad ) //重复用pad加在string开头,直到字串长度为length
rpad (string2 ,length ,pad) //在str后用pad补充,直到长度为length
LTRIM (string2 ) //去除前端空格
RTRIM (string2 ) //去除后端空格
repeat(string2 ,count ) //重复count次
mysql> select repeat('demacia',3); +-----------------------+ | repeat('demacia',3) | +-----------------------+ | demaciademaciademacia | +-----------------------+ 1 row in set
replace(str ,search_str ,replace_str ) //在str中用replace_str替换search_str
strcmp(string1 ,string2 ) //逐字符比较两字串大小,
mysql> select strcmp('demacia','wansui'); +----------------------------+ | strcmp('demacia','wansui') | +----------------------------+ | -1 | +----------------------------+ 1 row in set
注：mysql中处理字符串时，默认第一个字符下标为1，即参数position必须大于等于1
(2).数学类
ABS (number2 ) //绝对值
mysql> select abs(-1); +---------+ | abs(-1) | +---------+ | 1 | +---------+ 1 row in set
BIN (decimal_number ) //十进制转二进制
mysql> select bin(255); +----------+ | bin(255) | +----------+ | 11111111 | +----------+ 1 row in set
ceiling(number2 ) //向上取整
mysql> select ceiling(-12.5); +----------------+ | ceiling(-12.5) | +----------------+ | -12 | +----------------+ 1 row in set
floor(number2 ) //向下取整
mysql> select floor (-12.5); +--------------+ | floor(-12.5) | +--------------+ | -13 | +--------------+ 1 row in set
round (number [,decimals ]) //四舍五入,decimals为小数位数]
mysql> select round(3.654,1); +----------------+ | round(3.654,1) | +----------------+ | 3.7 | +----------------+ 1 row in set
conv(number2,from_base,to_base) //进制转换
mysql> select conv(255,10,2); +----------------+ | conv(255,10,2) | +----------------+ | 11111111 | +----------------+ 1 row in set
format(number,decimal_places ) //保留小数位数
mysql> select format(3.141592653,2); +-----------------------+ | format(3.141592653,2) | +-----------------------+ | 3.14 | +-----------------------+ 1 row in set
hex(DecimalNumber ) //转十六进制
mysql> select hex(255); +----------+ | hex(255) | +----------+ | FF | +----------+ 1 row in set
注：HEX()中可传入字符串，则返回其ASC-11码，如HEX('DEF')返回
444546
mysql> select hex('DEF'); +------------+ | hex('DEF') | +------------+ | 444546 | +------------+ 1 row in set
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
mysql> select least(1,3,5,-1,-2); +--------------------+ | least(1,3,5,-1,-2) | +--------------------+ | -2 | +--------------------+ 1 row in set
mod (numerator ,denominator ) //求余
mysql> select mod(5,2); +----------+ | mod(5,2) | +----------+ | 1 | +----------+ 1 row in set
power (number ,power ) //求指数
mysql> select power(2,7); +------------+ | power(2,7) | +------------+ | 128 | +------------+ 1 row in set
rand([seed]) //随机数
(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
mysql> select current_date(); +----------------+ | current_date() | +----------------+ | 2016-06-28 | +---------------
CURRENT_TIME ( ) //当前时间
mysql> select current_time(); +----------------+ | current_time() | +----------------+ | 17:04:10 | +----------------+ 1 row in set
CURRENT_TIMESTAMP ( ) //当前时间戳
mysql> select current_timestamp(); +---------------------+ | current_timestamp() | +---------------------+ | 2016-06-28 17:04:34 | +---------------------+ 1 row in set
DATE (datetime ) //返回datetime的日期部分
mysql> select date(current_timestamp); +-------------------------+ | date(current_timestamp) | +-------------------------+ | 2016-06-28 | +-------------------------+ 1 row in set
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
