学步园

1、确定某年某月有多少天

实现原理：先利用DATEDIFF取得当前月的第一天，再将月份加一取得下月第一天，然后减去1分钟，再取日期的

                   天数部分，即为当月最大日期，也即当月天数

CREATE FUNCTION DaysInMonth ( @date datetime ) Returns int
AS
BEGIN
 RETURN Day(dateadd(mi,-3,DATEADD(m, DATEDIFF(m,0,@date)+1,0)))
END

调用示例：

select dbo.DaysInMonth ('2006-02-03') 

(2)计算哪一天是本周的星期一

SELECT DATEADD(week, DATEDIFF(week,'1900-01-01',getdate()), '1900-01-01')  --返回2006-11-06 00:00:00.000
或
SELECT DATEADD(week, DATEDIFF(week,0,getdate()),0)     

(3)当前季度的第一天

SELECT DATEADD(quarter, DATEDIFF(quarter,0,getdate()), 0)—返回2006-10-01 00:00:00.000

(4)一个季度多少天

declare @m tinyint,@time smalldatetime

select @m=month(getdate())
select @m=case when @m between 1 and 3 then 1
                       when @m between 4 and 6 then 4
                       when @m between 7  and 9 then 7
                       else 10 end

select @time=datename(year,getdate())+'-'+convert(varchar(10),@m)+'-01'
select datediff(day,@time,dateadd(mm,3,@time)) —返回92

5）字符串转为数据类型(real，实数），自动截取数字转换

Alter FUNCTION ToNumeric (@str varchar(20)) RETURNS real
AS
BEGIN
 declare @temp char(1);
 declare @num varchar(20);
 declare @dot bit;
 declare @i int;
 declare @length int;

 set @num = '';
 set @dot = 0;
 set @i = 1;
 set @length = len(@str);
 
 set @temp = substring(@str,@i,1);

 while (isnumeric(@temp) = 1)
 begin
  set @num = @num + @temp;
  set @i = @i +1;
  set @temp = substring(@str,@i,1);
  
  if ('.' = @temp)
  begin
   if (1 = @dot)
    break;
   else
    set @dot = 1;
  end

 end

 return cast(@num as real);
END