年月日格式中两个日期之间的年龄总和

Question

I need to calculate age in years, months and days format between two dates ( DateFrom and DateTo ) in a way that:

• If day of month in DateFrom is 1st then take it as a whole month
• If day of month in DateFrom is not 1st then count days till the end of the month.

Example:

• DateFrom='2010-02-0 1 ', DateTo='2011-03-11', Age= 1 Years, 1 Months 11 Days
• DateFrom='2010-02-0 2 ', DateTo='2011-03-11', Age= 1 Years, 1 Months 8 Days

After calculating the age I'd need to sum the ages assuming that month is 30 days - in the above example I'd expect result: 2 Years, 2 Months, 19 Days.

Answer 1

My assumption would be that you have have a table containing " DateFrom " and " DateTo " columns so the query would be something like this:

DECLARE @TotalDiffInDays int = (SELECT AVG(DATEDIFF(DAY, DateFrom, DateTo)) AS [TotalDays] FROM #t)
SELECT @TotalDiffInDays
DECLARE @DaysInMonth int = 30;
DECLARE @DaysInYear int = 365;

SELECT 
    @TotalDiffInDays / 365 AS AvgYearsDiff, 
    (@TotalDiffInDays / @DaysInMonth  - @TotalDiffInDays / @DaysInYear * 12) AS AvgMonthsDiff,
    @TotalDiffInDays - ((@TotalDiffInDays / 365) * @DaysInYear + (@TotalDiffInDays / @DaysInMonth  - @TotalDiffInDays / @DaysInYear * 12) * @DaysInMonth) AS AvgDaysDiff

Note that in this case I am using INT division to get correct numbers.

In addition, if you just want to get dates difference in the format you desribed above you can use this query:

SELECT 
    DATEDIFF(YEAR, DateFrom, DateTo) AS [Years],
    -- Add year diff to get corret months diff 
    DATEDIFF(MONTH, DATEADD(YEAR, DATEDIFF(YEAR, DateFrom, DateTo), DateFrom), DateTo) AS [Months], 
    -- Add months diff to get correct days diff
    DATEDIFF(DAY, DATEADD(MONTH, DATEDIFF(MONTH, DateFrom, DateTo), DateFrom), DateTo) AS [Days]
FROM #t

I hope this will helps.

Yeah, just forgot about your rule of the 1st and not 1st day of the month, you can easily modify those queries with adding the DATEPART(DAY , your_date) function to check if it's a 1st date of the month and perform DETEADD() to apply this logic or just add a value of 1 before AVG.

Answer 2

So basically since this custom date maths, you'd need to implement your own functions to get desired results.

See the TSQL below

CREATE FUNCTION dbo.getDateSum(@d1 varchar(100),  @d2 varchar(100)) 
RETURNS varchar(100)
WITH EXECUTE AS CALLER
AS
BEGIN
    DECLARE @y int, @m int, @d int
    Select 
        @d1= REPLACE(REPLACE(REPLACE(@d1,' years, ', '-'),' months, ','-'),' days',''),
        @d2= REPLACE(REPLACE(REPLACE(@d2,' years, ', '-'),' months, ','-'),' days','')
    Select 
        @y= CAST(LEFT(@d1,CHARINDEX('-',@d1)-1) AS INT)+CAST(LEFT(@d2,CHARINDEX('-',@d2)-1) AS INT),
        @m= CAST(SUBSTRING(@d1,CHARINDEX('-',@d1)+1,LEN(@d1)-CHARINDEX('-',REVERSE(@d1))-CHARINDEX('-',@d1))AS INT)+CAST(SUBSTRING(@d2,CHARINDEX('-',@d2)+1,LEN(@d2)-CHARINDEX('-',REVERSE(@d2))-CHARINDEX('-',@d2)) AS INT),
        @d= CAST(LEFT(REVERSE(@d1),CHARINDEX('-',REVERSE(@d1))-1)AS INT)+CAST(LEFT(REVERSE(@d2),CHARINDEX('-',REVERSE(@d2))-1) AS INT)

    IF(@d>30)
    BEGIN
        SET @d=@d%30
        SET @m=@m+CAST(@d/30 as INT)
    END
    IF(@m>30)
    BEGIN
        SET @m=@m%12
        SET @y=@y+CAST(@m/12 as INT)
    END

    RETURN (cast(@y as varchar)+ ' years, ' + cast(@m as varchar) +' months, '+ cast(@d as varchar) + ' days' );
END
go


CREATE FUNCTION dbo.getDateDiff(@df date,  @dt date) 
RETURNS varchar(100)
WITH EXECUTE AS CALLER
AS
BEGIN
    declare @y int, @m int, @d int


    Select @y= YEAR(@dt)- YEAR(@df),@m= MONTH(@dt)- MONTH(@df),@d=CASE WHEN DAY(@df)=1 THEN DAY(@dt)- DAY(@df)+1 ELSE  DAY(@dt)- DAY(@df) -1 END
    If (@d<0) 
    BEGIN 
        Set @m=@m-1
        set @d=@d + DATEDIFF(d, @dt, EOMONTH(@dt))
    END
    IF(@m<0)
    BEGIN
        Set @y=@y-1
        Set @m=@m+ 12
    END

    RETURN (cast(@y as varchar)+ ' years, ' + cast(@m as varchar) +' months, '+ cast(@d as varchar) + ' days' )
END

go

SELECT dbo.getDateSum(dbo.getDateDiff('2010-02-01','2011-03-11'),dbo.getDateDiff('2010-02-02', '2011-03-11'))
go