SQL: How to produce next date given month and day - sql

Question

In my table I have a Month(tinyint) and a Day(tinyint) field. I would like to have a function that takes this month and day and produces a datetime for the next date(including year) given this month and day.
So if I had Month = 9, Day = 7 it would produce 9/7/2009.
If I had Month 1, Day 1 it would produce 1/1/2010.

Answer 1

something like this would work. It's variation on your method, but it doesn't use the MM/DD/YYYY literal format, and it won't blowup against bad input (for better or for worse).
declare #month tinyint
declare #day tinyint
set #month = 9
set #day = 1
declare #date datetime
-- this could be inlined if desired
set #date = convert(char(4),year(getdate()))+'0101'
set #date = dateadd(month,#month-1,#date)
set #date = dateadd(day,#day-1,#date)
if #date <= getdate()-1
set #date = dateadd(year,1,#date)
select #date
Alternatively, to create a string in YYYYMMDD format:
set #date =
right('0000'+convert(char(4),year(getdate())),4)
+ right('00'+convert(char(2),#month),2)
+ right('00'+convert(char(2),#day),2)
Another method, which avoids literals all together:
declare #month tinyint
declare #day tinyint
set #month = 6
set #day = 24
declare #date datetime
declare #today datetime
-- get todays date, stripping out the hours and minutes
-- and save the value for later
set #date = floor(convert(float,getdate()))
set #today = #date
-- add the appropriate number of months and days
set #date = dateadd(month,#month-month(#date),#date)
set #date = dateadd(day,#day-day(#date),#date)
-- increment year by 1 if necessary
if #date < #today set #date = dateadd(year,1,#date)
select #date

Answer 2

Here is my sql example so far. I don't really like it though...
DECLARE #month tinyint,
#day tinyint,
#date datetime
SET #month = 1
SET #day = 1
-- SET DATE TO DATE WITH CURRENT YEAR
SET #date = CONVERT(datetime, CONVERT(varchar,#month) + '/' + CONVERT(varchar,#day) + '/' + CONVERT(varchar,YEAR(GETDATE())))
-- IF DATE IS BEFORE TODAY, ADD ANOTHER YEAR
IF (DATEDIFF(DAY, GETDATE(), #date) < 0)
BEGIN
SET #date = DATEADD(YEAR, 1, #date)
END
SELECT #date

Answer 3

Here's a solution with PostgreSQL
your_date_calculated = Year * 10000 + Month * 100 + Day
gives you a date like 20090623.
select cast( cast( your_date_calculated as varchar ) as date ) + 1

Answer 4

Here's my version. The core of it is just two lines, using the DATEADD function, and it doesn't require any conversion to/from strings, floats or anything else:
DECLARE #Month TINYINT
DECLARE #Day TINYINT
SET #Month = 9
SET #Day = 7
DECLARE #Result DATETIME
SET #Result =
DATEADD(month, ((YEAR(GETDATE()) - 1900) * 12) + #Month - 1, #Day - 1)
IF (#Result < GETDATE())
SET #Result = DATEADD(year, 1, #Result)
SELECT #Result