使用Datediff和DatePart的Case语句

Question

有人可以帮助一个案例陈述，我需要的是查询显示如下所示。我知道有更简单的方法可以做到这一点，但我只是需要关于Case语句的帮助。

--如果当前月份‘小于’道布月份，则从总年数中取‘1’等于41。--如果当前月份‘大于’道布的月份，则年龄是正确的。--但是，如果当前月份与道布月份“相等”，则我们需要转到“日”级别以获取正确的年龄。

Set @DOB = '01 November 1971'
Set @Today = GETDATE()


SELECT Datediff(Year,@DOB,@Today) AS Years, 
Datepart(Month,@DOB) As DOB_Month, 
Datepart(Day, @DOB) as DOB_Day,
DatePart(Month, @Today) As Current_Month, 
Datepart(Day,@Today) AS Current_Day

Answer 1

试试这个：

DECLARE @DOB DATE= '01 November 1971'
DECLARE @TODAY DATE = GETDATE()

SELECT CASE 
WHEN DATEPART(MONTH, @TODAY) < DATEPART(MONTH,@DOB) THEN DATEDIFF(YEAR,@DOB,@TODAY) - 1
WHEN DATEPART(MONTH, @TODAY) > DATEPART(MONTH,@DOB) THEN DATEDIFF(YEAR,@DOB,@TODAY)
ELSE
    CASE 
         WHEN DATEPART(DAY, @TODAY) < DATEPART(DAY,@DOB) THEN DATEDIFF(YEAR,@DOB,@TODAY) - 1
         ELSE DATEDIFF(YEAR,@DOB,@TODAY)  
    END       
END

Answer 2

您可以尝试这样做：

case 
    when DatePart(Month, @Today)  > Datepart(Month,@DOB) then Datediff(Year,@DOB,@Today) 
    when DatePart(Month, @Today)  < Datepart(Month,@DOB) then (Datediff(Year,@DOB,@Today) - 1)
    when DatePart(Month, @Today)  = Datepart(Month,@DOB) then 
        case 
            when DatePart(Day, @Today)  >= Datepart(Day,@DOB) then (Datediff(Year,@DOB,@Today) )
            when DatePart(Day, @Today)  < Datepart(Day,@DOB) then (Datediff(Year,@DOB,@Today) - 1 )
        end
end as AgeCompleted,

Answer 3

declare @DOB date = '19680411'
select datediff(year, @DOB, getdate())- case when month(@DOB)*32 + day(@DOB) > 
month(getdate()) * 32 + day(getdate()) then 1 else 0 end