mysql bin函数_MySQL之函数
了解编程的人一般都会知道函数的重要性，丰富的函数有的时候可以给我们带来事半功倍的效果，在MySQL中提供了许多的内置函数，能够帮助开发人员编写简单快捷的SQL语句,除了这些内置的函数之外，用户也可以自定义函数，本次博客整理了一下MySQL中常用的函数，简单的介绍了自定函数，MySQL版本mysql-5.7.19。
常用函数
1.字符串函数
字符串函数是最常用的一种函数。下表列出了常用的字符串函数：
2.数值函数
MySQL中另外一类就是数值函数了。这些函数可以处理很多数值方面的运算，常见的数值运算函数如下：
3.日期和时间函数
有的时候们需要了解当前的时间，这时候我们就可以调用时间函数了。下面就是一些常用的时间函数：
下面来说一下DATE_FORMAT(date,format)：format可以有以下格式符：
Specifier Description%a Abbreviated weekday name (Sun..Sat)%b Abbreviated month name (Jan..Dec)%c Month, numeric (0..12)%D Day of the month with English suffix (0th, 1st, 2nd, 3rd, …)%d Day of the month, numeric (00..31)%e Day of the month, numeric (0..31)%f Microseconds (000000..999999)%H Hour (00..23)%h Hour (01..12)%I Hour (01..12)%i Minutes, numeric (00..59)%j Day of year (001..366)%k Hour (0..23)%l Hour (1..12)%M Month name (January..December)%m Month, numeric (00..12)%p AM or PM%r Time, 12-hour (hh:mm:ss followed by AM or PM)%S Seconds (00..59)%s Seconds (00..59)%T Time, 24-hour (hh:mm:ss)%U Week (00..53), where Sunday is the first day of the week; WEEK() mode 0
%u Week (00..53), where Monday is the first day of the week; WEEK() mode 1
%V Week (01..53), where Sunday is the first day of the week; WEEK() mode 2; used with %X%v Week (01..53), where Monday is the first day of the week; WEEK() mode 3; used with %x%W Weekday name (Sunday..Saturday)%w Day of the week (0=Sunday..6=Saturday)%X Year for the week where Sunday is the first day of the week, numeric, four digits; used with %V%x Year for the week, where Monday is the first day of the week, numeric, four digits; used with %v%Y Year, numeric, four digits%y Year, numeric (two digits)%% A literal %character%x x, for any “x” not listed above
格式符
举个例子吧！
mysql> SELECT DATE_FORMAT('2009-10-04 22:23:00', '%W %M %Y');+------------------------------------------------+
| DATE_FORMAT('2009-10-04 22:23:00', '%W %M %Y') |
+------------------------------------------------+
| Sunday October 2009 |
+------------------------------------------------+
1 row in set (0.00sec)
mysql> SELECT DATE_FORMAT(now(),'%H %k %I %r %T %S %w');+-------------------------------------------+
| DATE_FORMAT(now(),'%H %k %I %r %T %S %w') |
+-------------------------------------------+
| 23 23 11 11:49:57 PM 23:49:57 57 5 |
+-------------------------------------------+
1 row in set (0.00 sec)
再来看一下DATE_ADD(date,INTERVAL expr unit)：其中INTERVAL是关键字，expr是一个表达式，unit为间隔类型，MySQL提供如下的间隔类型:
unit Value Expected expr Format
MICROSECOND MICROSECONDS
SECOND SECONDS
MINUTE MINUTES
HOUR HOURSDAYDAYS
WEEK WEEKSMONTHMONTHS
QUARTER QUARTERSYEARYEARS
SECOND_MICROSECOND'SECONDS.MICROSECONDS'MINUTE_MICROSECOND'MINUTES:SECONDS.MICROSECONDS'MINUTE_SECOND'MINUTES:SECONDS'HOUR_MICROSECOND'HOURS:MINUTES:SECONDS.MICROSECONDS'HOUR_SECOND'HOURS:MINUTES:SECONDS'HOUR_MINUTE'HOURS:MINUTES'DAY_MICROSECOND'DAYS HOURS:MINUTES:SECONDS.MICROSECONDS'DAY_SECOND'DAYS HOURS:MINUTES:SECONDS'DAY_MINUTE'DAYS HOURS:MINUTES'DAY_HOUR'DAYS HOURS'YEAR_MONTH'YEARS-MONTHS'
间隔类型
举个例子吧！
mysql> SELECT DATE_ADD('2000-12-31 23:59:59',INTERVAL 1SECOND);+---------------------------------------------------+
| DATE_ADD('2000-12-31 23:59:59',INTERVAL 1 SECOND) |
+---------------------------------------------------+
| 2001-01-01 00:00:00 |
+---------------------------------------------------+
1 row in set (0.00sec)
mysql> SELECT DATE_ADD('2100-12-31 23:59:59',INTERVAL '1:1'MINUTE_SECOND);+--------------------------------------------------------------+
| DATE_ADD('2100-12-31 23:59:59',INTERVAL '1:1' MINUTE_SECOND) |
+--------------------------------------------------------------+
| 2101-01-01 00:01:00 |
+--------------------------------------------------------------+
1 row in set (0.00 sec)
4.流程函数
流程函数也是很常用的一类函数，用户可以使用这类函数在一个SQL语句中实现条件选择，这样做能够提高语句的效率。
举例：
现在有员工工资表如下：
mysql> select * fromsalary;+----+---------+
| id | salary |
+----+---------+
| 1 | 1000.00 |
| 2 | 2000.00 |
| 3 | 3000.00 |
| 4 | 4000.00 |
| 5 | 5000.00 |
| 6 | 6000.00 |
| 7 | 7000.00 |
| 8 | NULL |
+----+---------+
8 rows in set (0.00 sec)
(1)当工资高于5000就显示高工资，低于5000的就显示低工资：
mysql> select id,if(salary>5000,'高工资','低工资') as level fromsalary;+----+-----------+
| id | level |
+----+-----------+
| 1 | 低工资 |
| 2 | 低工资 |
| 3 | 低工资 |
| 4 | 低工资 |
| 5 | 低工资 |
| 6 | 高工资 |
| 7 | 高工资 |
| 8 | 低工资 |
+----+-----------+
8 rows in set (0.00 sec)
View Code
(2)当没有工资的时候，用0代替：
mysql> select ifnull(salary,0) fromsalary;+------------------+
| ifnull(salary,0) |
+------------------+
| 1000.00 |
| 2000.00 |
| 3000.00 |
| 4000.00 |
| 5000.00 |
| 6000.00 |
| 7000.00 |
| 0.00 |
+------------------+
8 rows in set (0.00 sec)
View Code
(3)用case when来实现例子1：
mysql> select id,case when salary>5000 then '高工资' else '低工资' end fromsalary;+----+-------------------------------------------------------------+
| id | case when salary>5000 then '高工资' else '低工资' end |
+----+-------------------------------------------------------------+
| 1 | 低工资 |
| 2 | 低工资 |
| 3 | 低工资 |
| 4 | 低工资 |
| 5 | 低工资 |
| 6 | 高工资 |
| 7 | 高工资 |
| 8 | 低工资 |
+----+-------------------------------------------------------------+
8 rows in set (0.00 sec)
View Code
(4)当工资是1000的为特低工资，工资为2000的为低工资，其余为高工资：
mysql> select id,case salary when 1000 then '特低工资' when 2000 then '低工资' else '高工资' end fromsalary;+----+-------------------------------------------------------------------------------------------+
| id | case salary when 1000 then '特低工资' when 2000 then '低工资' else '高工资' end |
+----+-------------------------------------------------------------------------------------------+
| 1 | 特低工资 |
| 2 | 低工资 |
| 3 | 高工资 |
| 4 | 高工资 |
| 5 | 高工资 |
| 6 | 高工资 |
| 7 | 高工资 |
| 8 | 高工资 |
+----+-------------------------------------------------------------------------------------------+
8 rows in set (0.00 sec)
View Code
5.其他函数
自定义函数
用户可以自定义函数，语法如下：
CREATE FUNCTION func_name([parameter1,parameter2...])RETURNStype
runtime_body
下面就来创建一个函数，比如自定义一个两个整数的加法函数：
DELIMITER $CREATE FUNCTION mysum(n1 INT,n2 INT) RETURNS INT
BEGIN
DECLARE num int DEFAULT 0;SET num = n1 +n2;RETURN(NUM);END$
DELIMITER ;
执行函数使用SELECT：
mysql> SELECT mysum(1,2);+------------+
| mysum(1,2) |
+------------+
| 3 |
+------------+
1 row in set (0.00 sec)
删除自定函数使用:
DROP FUNCTION func_name
比如删除上面创建的函数：
mysql> drop functionmysum;
Query OK,0 rows affected (0.00 sec)
自定义函数暂时写到这里，更详细的会在下一篇博客中和存储过程一起介绍。