Adding Days To Date in SQL - sql-server

Question

I am trying to get data from my Database of those who have upcoming birth days in next few days(declared earlier)
it's working fine for days but this query will not work if i add 24 days to current date cause than it will need change in month.
i wonder how can i do it
declare #date int=10,
#month int=0
select * from STUDENT_INFO where DATEPART(DD,STDNT_DOB) between
DATEPART(DD,GETDATE()) and DATEPART(DD,DATEADD(DD,#date,GETDATE()))
and
DATEPART(MM,STDNT_DOB) = DATEPART(MM,DATEADD(MM,#month,GETDATE()))
This query works fine but it only checks date between 8 & 18
but if i use it like this
declare #date int=30,
#month int=0
select * from STUDENT_INFO where DATEPART(DD,STDNT_DOB) between
DATEPART(DD,GETDATE()) and DATEPART(DD,DATEADD(DD,#date,GETDATE()))
and
DATEPART(MM,STDNT_DOB) = DATEPART(MM,DATEADD(MM,#month,GETDATE()))
it will return nothing since it require addition in month as well
If I Use it like this
declare #date int=40,
#month int=0
select * from STUDENT_INFO where DATEPART(DD,STDNT_DOB) between
DATEPART(DD,GETDATE()) and DATEADD(DD,#date,GETDATE())
and
DATEPART(MM,STDNT_DOB) = DATEPART(MM,DATEADD(MM,#month,GETDATE()))
than it will return results till the last of this month but will not show till 18/12 which was required

Answer 1

Here is a simple way to solve it:
DECLARE #date int = 10
;WITH cte as
(
SELECT cast(getdate() as date) fromdate,
cast(getdate() as date) todate,
1 loop
UNION ALL
SELECT cast(dateadd(year, -loop, getdate()) as date),
cast(dateadd(year, -loop, getdate())+#date as date),
loop+1
FROM cte
WHERE loop < 200 -- go back 200 years
-- (should be enough unless you are a turtle)
)
SELECT dob, name, datediff(year, dob, getdate()) will_turn
FROM cte
JOIN (values(cast('1968-11-11' as date), 'Jack'),
(cast('1984-11-12' as date), 'Jill'),
(cast('1984-11-13' as date), 'Hans'),
(cast('1984-11-21' as date), 'Gretchen'),
(cast('1884-11-22' as date), 'Snowwhite')) x(dob, name)
ON dob BETWEEN fromdate and todate
OPTION (maxrecursion 300)
Returns:
dob name name will_turn
1984-11-12 Jill 29
1984-11-13 Hans 29
1984-11-21 Gretchen 29
1968-11-11 Jack 45

Answer 2

avoiding udf:-
create table #dob (
name varchar(50),
cakeday date
)
go
insert into #dob values
('yesterday',dateadd(yy,-50,getdate()-1)),
('today',dateadd(yy,-51,getdate())),
('ten days',dateadd(yy,-52,getdate()+10)),
('eleven days',dateadd(yy,-53,getdate()+11))
go
select *
from #dob d
where datepart(dayofyear,d.cakeday)
between datepart(dayofyear,getdate()) and datepart(dayofyear,getdate())+10
returns (on 2013-11-09):-
name cakeday
today 1962-11-09
ten days 1961-11-19

Answer 3

Would this work for you?
declare #date int = 10
select * from STUDENT_INFO
where DATEDIFF(DD, GETDATE(),
DATEFROMPARTS(DATEPART(YYYY, GETDATE()), -- this years birthday
DATEPART(MM, STDNT_DOB),
DATEPART(DD, STDNT_DOB))) between 0 and #date
or DATEDIFF(DD, GETDATE(),
DATEFROMPARTS(DATEPART(YYYY, GETDATE()) + 1, -- next years birthday
DATEPART(MM, STDNT_DOB),
DATEPART(DD, STDNT_DOB))) between 0 and #date
The trick here is to get the students birthday this year (and next year) and get the number of days until that date. I did that by creating a calculated field using the students day and month of birth, and included todays year.
The check against next years birthday (i.e., the second part of the OR clause) is required to get those students whose upcoming birthday is early next year.
Edit: the query will fail if anyone on the table was born on feb/29 (on a leap year, of course). Thanks to t-clausen.dk for poiting it out.