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mysql常用函数

Jun 07, 2016 pm 04:38 PM
abs b mysql function Commonly used math absolute value return

一、数学函数 ABS(x)?? 返回x的绝对值 BIN(x)?? 返回x的二进制(OCT返回八进制,HEX返回十六进制) CEILING(x)? ? 返回大于x的最小整数值 EXP(x)?? 返回值e(自然对数的底)的x次方 FLOOR(x)?? 返回小于x的最大整数值 GREATEST(x1,x2,,xn)返回集合中最大的值

一、数学函数
ABS(x)?? 返回x的绝对值

BIN(x)?? 返回x的二进制(OCT返回八进制,HEX返回十六进制)
CEILING(x)?? 返回大于x的最小整数值
EXP(x)?? 返回值e(自然对数的底)的x次方
FLOOR(x)?? 返回小于x的最大整数值
GREATEST(x1,x2,…,xn)返回集合中最大的值
LEAST(x1,x2,…,xn)??????返回集合中最小的值
LN(x)????????????????????返回x的自然对数
LOG(x,y)返回x的以y为底的对数
MOD(x,y)?????????????????返回x/y的模(余数)
PI()返回pi的值(圆周率)
RAND()返回0到1内的随机值,可以通过提供一个参数(种子)使RAND()随机数生成器生成一个指定的值。
ROUND(x,y)返回参数x的四舍五入的有y位小数的值
SIGN(x) 返回代表数字x的符号的值
SQRT(x) 返回一个数的平方根
TRUNCATE(x,y)????????????返回数字x截短为y位小数的结果

二、聚合函数(常用于GROUP BY从句的SELECT查询中)
AVG(col)返回指定列的平均值
COUNT(col)返回指定列中非NULL值的个数
MIN(col)返回指定列的最小值
MAX(col)返回指定列的最大值
SUM(col)返回指定列的所有值之和
GROUP_CONCAT(col) 返回由属于一组的列值连接组合而成的结果

三、字符串函数
ASCII(char)返回字符的ASCII码值
BIT_LENGTH(str)返回字符串的比特长度
CONCAT(s1,s2…,sn)将s1,s2…,sn连接成字符串
CONCAT_WS(sep,s1,s2…,sn)将s1,s2…,sn连接成字符串,并用sep字符间隔
INSERT(str,x,y,instr) 将字符串str从第x位置开始,y个字符长的子串替换为字符串instr,返回结果
FIND_IN_SET(str,list)分析逗号分隔的list列表,如果发现str,返回str在list中的位置
LCASE(str)或LOWER(str) 返回将字符串str中所有字符改变为小写后的结果
LEFT(str,x)返回字符串str中最左边的x个字符
LENGTH(s)返回字符串str中的字符数
LTRIM(str) 从字符串str中切掉开头的空格
POSITION(substr,str) 返回子串substr在字符串str中第一次出现的位置
QUOTE(str) 用反斜杠转义str中的单引号
REPEAT(str,srchstr,rplcstr)返回字符串str重复x次的结果
REVERSE(str) 返回颠倒字符串str的结果
RIGHT(str,x) 返回字符串str中最右边的x个字符
RTRIM(str) 返回字符串str尾部的空格
STRCMP(s1,s2)比较字符串s1和s2
TRIM(str)去除字符串首部和尾部的所有空格
UCASE(str)或UPPER(str) 返回将字符串str中所有字符转变为大写后的结果

四、日期和时间函数
CURDATE()或CURRENT_DATE() 返回当前的日期
CURTIME()或CURRENT_TIME() 返回当前的时间
DATE_ADD(date,INTERVAL int keyword)返回日期date加上间隔时间int的结果(int必须按照关键字进行格式化),如:SELECTDATE_ADD(CURRENT_DATE,INTERVAL 6 MONTH);
DATE_FORMAT(date,fmt)??依照指定的fmt格式格式化日期date值
DATE_SUB(date,INTERVAL int keyword)返回日期date加上间隔时间int的结果(int必须按照关键字进行格式化),如:SELECTDATE_SUB(CURRENT_DATE,INTERVAL 6 MONTH);
DAYOFWEEK(date)???返回date所代表的一星期中的第几天(1~7)
DAYOFMONTH(date)??返回date是一个月的第几天(1~31)
DAYOFYEAR(date)???返回date是一年的第几天(1~366)
DAYNAME(date)???返回date的星期名,如:SELECT DAYNAME(CURRENT_DATE);
FROM_UNIXTIME(ts,fmt)??根据指定的fmt格式,格式化UNIX时间戳ts
HOUR(time)???返回time的小时值(0~23)
MINUTE(time)???返回time的分钟值(0~59)
MONTH(date)???返回date的月份值(1~12)
MONTHNAME(date)???返回date的月份名,如:SELECT MONTHNAME(CURRENT_DATE);
NOW()????返回当前的日期和时间
QUARTER(date)???返回date在一年中的季度(1~4),如SELECT QUARTER(CURRENT_DATE);
WEEK(date)???返回日期date为一年中第几周(0~53)
YEAR(date)???返回日期date的年份(1000~9999)
一些示例:
获取当前系统时间:SELECT FROM_UNIXTIME(UNIX_TIMESTAMP());
SELECT EXTRACT(YEAR_MONTH FROM CURRENT_DATE);
SELECT EXTRACT(DAY_SECOND FROM CURRENT_DATE);
SELECT EXTRACT(HOUR_MINUTE FROM CURRENT_DATE);
返回两个日期值之间的差值(月数):SELECT PERIOD_DIFF(200302,199802);
在Mysql中计算年龄:
SELECT DATE_FORMAT(FROM_DAYS(TO_DAYS(NOW())-TO_DAYS(birthday)),’%Y’)+0 AS age FROM employee;
这样,如果Brithday是未来的年月日的话,计算结果为0。
下面的SQL语句计算员工的绝对年龄,即当Birthday是未来的日期时,将得到负值。
SELECT DATE_FORMAT(NOW(), ‘%Y’) – DATE_FORMAT(birthday, ‘%Y’) -(DATE_FORMAT(NOW(), ’00-%m-%d’)

五、加密函数
AES_ENCRYPT(str,key)??返回用密钥key对字符串str利用高级加密标准算法加密后的结果,调用AES_ENCRYPT的结果是一个二进制字符串,以BLOB类型存储
AES_DECRYPT(str,key)??返回用密钥key对字符串str利用高级加密标准算法解密后的结果
DECODE(str,key)???使用key作为密钥解密加密字符串str
ENCRYPT(str,salt)???使用UNIXcrypt()函数,用关键词salt(一个可以惟一确定口令的字符串,就像钥匙一样)加密字符串str
ENCODE(str,key)???使用key作为密钥加密字符串str,调用ENCODE()的结果是一个二进制字符串,它以BLOB类型存储
MD5()????计算字符串str的MD5校验和
PASSWORD(str)???返回字符串str的加密版本,这个加密过程是不可逆转的,和UNIX密码加密过程使用不同的算法。
SHA()????计算字符串str的安全散列算法(SHA)校验和
示例:
SELECT ENCRYPT(‘root’,'salt’);
SELECT ENCODE(‘xufeng’,'key’);
SELECT DECODE(ENCODE(‘xufeng’,'key’),’key’);#加解密放在一起
SELECT AES_ENCRYPT(‘root’,'key’);
SELECT AES_DECRYPT(AES_ENCRYPT(‘root’,'key’),’key’);
SELECT MD5(’123456′);
SELECT SHA(’123456′);

六、控制流函数
MySQL有4个函数是用来进行条件操作的,这些函数可以实现SQL的条件逻辑,允许开发者将一些应用程序业务逻辑转换到数据库后台。
MySQL控制流函数:
CASE WHEN[test1] THEN [result1]…ELSE [default] END如果testN是真,则返回resultN,否则返回default
CASE [test] WHEN[val1] THEN [result]…ELSE [default]END??如果test和valN相等,则返回resultN,否则返回default
IF(test,t,f)???如果test是真,返回t;否则返回f
IFNULL(arg1,arg2) 如果arg1不是空,返回arg1,否则返回arg2
NULLIF(arg1,arg2) 如果arg1=arg2返回NULL;否则返回arg1
这些函数的第一个是IFNULL(),它有两个参数,并且对第一个参数进行判断。如果第一个参数不是NULL,函数就会向调用者返回第一个参数;如果是NULL,将返回第二个参数。
如:SELECT IFNULL(1,2), IFNULL(NULL,10),IFNULL(4*NULL,’false’);
NULLIF()函数将会检验提供的两个参数是否相等,如果相等,则返回NULL,如果不相等,就返回第一个参数。
如:SELECT NULLIF(1,1),NULLIF(‘A’,'B’),NULLIF(2+3,4+1);
和许多脚本语言提供的IF()函数一样,MySQL的IF()函数也可以建立一个简单的条件测试,这个函数有三个参数,第一个是要被判断的表达式,如果表达式为真,IF()将会返回第二个参数,如果为假,IF()将会返回第三个参数。
如:SELECTIF(1100,’true’,'false’);
IF()函数在只有两种可能结果时才适合使用。然而,在现实世界中,我们可能发现在条件测试中会需要多个分支。在这种情况下,MySQL提供了CASE函数,它和PHP及Perl语言的switch-case条件例程一样。
CASE函数的格式有些复杂,通常如下所示:
CASE [expression to be evaluated]
WHEN [val 1] THEN [result 1]
WHEN [val 2] THEN [result 2]
WHEN [val 3] THEN [result 3]
……
WHEN [val n] THEN [result n]
ELSE [default result]
END
这里,第一个参数是要被判断的值或表达式,接下来的是一系列的WHEN-THEN块,每一块的第一个参数指定要比较的值,如果为真,就返回结果。所有的WHEN-THEN块将以ELSE块结束,当END结束了所有外部的CASE块时,如果前面的每一个块都不匹配就会返回ELSE块指定的默认结果。如果没有指定ELSE块,而且所有的WHEN-THEN比较都不是真,MySQL将会返回NULL。
CASE函数还有另外一种句法,有时使用起来非常方便,如下:
CASE
WHEN [conditional test 1] THEN [result 1]
WHEN [conditional test 2] THEN [result 2]
ELSE [default result]
END
这种条件下,返回的结果取决于相应的条件测试是否为真。
示例:
mysql>SELECT CASE ‘green’
????WHEN ‘red’ THEN ‘stop’
????WHEN ‘green’ THEN ‘go’ END;
SELECT CASE 9 WHEN 1 THEN ‘a’ WHEN 2 THEN ‘b’ ELSE ‘N/A’ END;
SELECT CASE WHEN (2+2)=4 THEN ‘OK’ WHEN(2+2)4 THEN ‘not OK’ END ASSTATUS;
SELECT Name,IF((IsActive = 1),’已激活’,'未激活’) AS RESULT FROMUserLoginInfo;
SELECT fname,lname,(math+sci+lit) AS total,
CASE WHEN (math+sci+lit) WHEN (math+sci+lit) BETWEEN 50 AND 150 THEN ‘C’
WHEN (math+sci+lit) BETWEEN 151 AND 250 THEN ‘B’
ELSE ‘A’ END
AS grade FROM marks;
SELECT IF(ENCRYPT(‘sue’,'ts’)=upass,’allow’,'deny’) AS LoginResultFROM users WHERE uname = ‘sue’;#一个登陆验证

七、格式化函数
DATE_FORMAT(date,fmt)??依照字符串fmt格式化日期date值
FORMAT(x,y)???把x格式化为以逗号隔开的数字序列,y是结果的小数位数
INET_ATON(ip)???返回IP地址的数字表示
INET_NTOA(num)???返回数字所代表的IP地址
TIME_FORMAT(time,fmt)??依照字符串fmt格式化时间time值
其中最简单的是FORMAT()函数,它可以把大的数值格式化为以逗号间隔的易读的序列。
示例:
SELECT FORMAT(34234.34323432,3);
SELECT DATE_FORMAT(NOW(),’%W,%D %M %Y %r’);
SELECT DATE_FORMAT(NOW(),’%Y-%m-%d’);
SELECT DATE_FORMAT(19990330,’%Y-%m-%d’);
SELECT DATE_FORMAT(NOW(),’%h:%i %p’);
SELECT INET_ATON(’10.122.89.47′);
SELECT INET_NTOA(175790383);

八、类型转化函数
为了进行数据类型转化,MySQL提供了CAST()函数,它可以把一个值转化为指定的数据类型。类型有:BINARY,CHAR,DATE,TIME,DATETIME,SIGNED,UNSIGNED
示例:
SELECT CAST(NOW() AS SIGNED INTEGER),CURDATE()+0;
SELECT ‘f’=BINARY ‘F’,'f’=CAST(‘F’ AS BINARY);

九、系统信息函数
DATABASE()???返回当前数据库名
BENCHMARK(count,expr)??将表达式expr重复运行count次
CONNECTION_ID()???返回当前客户的连接ID
FOUND_ROWS()???返回最后一个SELECT查询进行检索的总行数
USER()或SYSTEM_USER()??返回当前登陆用户名
VERSION()???返回MySQL服务器的版本
示例:
SELECT DATABASE(),VERSION(),USER();
SELECTBENCHMARK(9999999,LOG(RAND()*PI()));#该例中,MySQL计算LOG(RAND()*PI())表达式9999999次。

FROM:http://blog.csdn.net/sugang_ximi/article/details/6664748

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