Getting FRACTIONAL difference (YEARS) between two dates in T SQL - sql

Question

I need to detect a difference between two dates, such that when Date_1 = 12-jan-2010 and Date_2 = 01-jan-2016 I would NOT get 6 but a number < 6.
SELECT DATEDIFF(YEAR,'12-jan-2010','01-jan-2016')
DATEDIFF returns 6 in the above case.

Answer 1

It depends on required precision, try following:
SELECT DATEDIFF(DAY, #d1, #d2)/365.25

Answer 2

I guess this resolves,
DECLARE #STARTDATE DATE='12-jan-2010'
DECLARE #ENDDATE DATE='01-jan-2016'
DECLARE #TOTALDAY DECIMAL(18,2)=DATEDIFF(day,#STARTDATE,#ENDDATE)
DECLARE #AVGYEAR DECIMAL(18,2)= ((365*DATEDIFF(YEAR,#STARTDATE,#ENDDATE))+
dbo.LEAP_YEAR(#STARTDATE,#ENDDATE))/CONVERT(DECIMAL(18,2),
DATEDIFF(YEAR,#STARTDATE,#ENDDATE))
SELECT CONVERT(decimal(18,2),#TOTALDAY/#AVGYEAR) AS DiffDate ---This will provide you result in decimal
this the function which return no of leap years between dates.
ALTER FUNCTION LEAP_YEAR(#START DATE,#END DATE)
RETURNS INT
AS BEGIN
DECLARE #COUNT INT = 0,#Z INT = DATEPART(YYYY,#START)
DECLARE #X INT =DATEPART(YYYY,#START)
DECLARE #Y INT =DATEPART(YYYY,#END)
IF (DATEPART(MM,#START) >2)
SET #X=#X+1
IF (DATEPART(MM,#END) <2)
SET #Y=#Y-1
WHILE (#X <= #Y)
BEGIN
SET #COUNT = #COUNT +
(CASE WHEN (#X%4 = 0 AND #X%100 !=0) OR #X%400 = 0
THEN 1
ELSE 0 END)
SET #X = #X + 1
END
RETURN #COUNT
END

Answer 3

If I've got it right. Just Add result of DATEDIFF (6 in this case) to the start date if it > the end date then just subtract 1 year so you will get 5 full years:
DECLARE #StartD DATETIME;
DECLARE #FinalD DATETIME;
SET #StartD = '12-jan-2010';
SET #FinalD = '11-jan-2016';
SELECT DATEDIFF(YEAR,#StartD,#FinalD)
- CASE WHEN DATEADD(YEAR,DATEDIFF(YEAR,#StartD,#FinalD),#StartD)>#FinalD
THEN 1 ELSE 0 END

Answer 4

First of all, I wish to thank all those that spent time trying to provide a simple and reliable solution. Finally, I decided to resolve it as follows:
Supposed that I want to know if #n full years passed between two dates, then:
DECLARE #n INT ;
DECLARE #Old_Date DATETIME ;
DECLARE #New_Date DATETIME ;
SET #n = <some_value> ;
SET #Old_Date = <some_value> ;
SET #New_Date = <some_value> ;
IF (DATEADD(YEAR ,#n , #Old_Date) <= #New_Date)
SET #Result = 'YES' ;
ELSE
SET #Result = 'NO' ;
[of course, a check needs to be included to verify that #Old_Date < #New_Date]
I can't say this can be proved (mathematically) as correct in all possible scenarios, but it provides the needed answer to me.
Thanks to all again.