Computed Column Date Leap Year issue - sql

Question

I have a table of names and associated birthdates. I can retrieve the names of everyone whose birthday is today by matching the MONTH and DAY dateparts between the birthdate in the database and the current date. However, I need to pull "looking forward" lists of, say, all birthdays in the next two weeks.
The obvious solution would be a computed column for each person, showing his/her "birthday this year". It's easy to pull the month and day from the birthday, add the current year, and cast the whole string as a date. That way I could just retrieve those whose "birthday this year" is within X days of the current date. However, I have one person with a birthday on February 29, and there isn't a Feb. 29 every year, so the calculated column "chokes" when I query or open the table with the following error:
The conversion of a char data type to a datetime data type resulted in an out-of-range datetime value.
Suggestions on a way to either make a computed column work properly in this situation, or an alternative way to query using the date of birth in the table?

Answer 1

Change your query from using convert to using try_convert which will not error on nonexistent date but will instead return NULL. This will exclude your Feb 29 birthday client if running year is not leap.

Answer 2

Your approach won't work for the end of December, because the year changes. Here is a different approach:
Add the number of years to the date and let the database handle leap years.
Then do the comparison.
So, the logic for the first is:
select dateadd(year, year(getdate()) - year(dob), dob)
Then to get dates of birth in the next two weeks:
where dateadd(year, year(getdate()) - year(dob), dob) >= convert(date, getdate()) and
dateadd(year, year(getdate()) - year(dob), dob) < dateadd(14, day, convert(date, getdate())
However, this still doesn't handle dates of birth that could be next year. So, to handle the end of year, consider that as well:
where (dateadd(year, year(getdate()) - year(dob), dob) >= convert(date, getdate()) and
dateadd(year, year(getdate()) - year(dob), dob) < dateadd(14, day, convert(date, getdate())
) or
(dateadd(year, 1 + year(getdate()) - year(dob), dob) >= convert(date, getdate()) and
dateadd(year, 1 + year(getdate()) - year(dob), dob) < dateadd(14, day, convert(date, getdate())
)

Answer 3

To do this - you need to calculate the current year's DOB and the persons next date of birth. To calculate the current year date of birth we can use a simple calculation:
dateadd(year, datediff(year, DateOfBirth, CurrentDate), DateOfBirth)
Then - we need to calculate the next date of birth, which is simply adding a year if the current year DOB is less than CurrentDate:
dateadd(year, iif(CurrentDOB < CurrentDate, 1, 0), CurrentDOB)
Now - it is just a matter of checking if the next DOB is in the range. Here is some sample data to show how to put this together.
--==== Some sample dates of birth - including leap year DOB's
Declare #testData Table (DateOfBirth date);
Insert Into #testData (DateOfBirth)
Values ('1992-01-09'), ('2020-02-29'), ('1965-09-30'), ('1984-02-29');
--==== Test using different dates
Declare #current_date date = '2021-02-28';
--==== Use CROSS APPLY to calculate current year DOB and Next DOB
Select *
From #testData As td
Cross Apply (Values (dateadd(year, datediff(year, td.DateOfBirth, #current_date), td.DateOfBirth))) As y(CurrentDOB)
Cross Apply (Values (dateadd(year, iif(y.CurrentDOB < #current_date, 1, 0), y.CurrentDOB))) As n(NextDOB)
Where n.NextDOB <= dateadd(day, 14, #current_date);
If today is 2021-02-28 then the birthdays that fall on the 29th will be included. If today is 2021-03-01 then those will not be included because they would be calculated as 2022-02-28 which is not within 14 days.