How to calculate age (in years) based on Date of Birth and getDate()

Question

I have a table listing people along with their date of birth (currently a nvarchar(25))

How can I convert that to a date, and then calculate their age in years?

Answer 1

Since there isn't one simple answer that always gives the correct age, here's what I came up with.

SELECT DATEDIFF(YY, DateOfBirth, GETDATE()) - 
     CASE WHEN RIGHT(CONVERT(VARCHAR(6), GETDATE(), 12), 4) >= 
               RIGHT(CONVERT(VARCHAR(6), DateOfBirth, 12), 4) 
     THEN 0 ELSE 1 END AS AGE 

This gets the year difference between the birth date and the current date. Then it subtracts a year if the birthdate hasn't passed yet.

Accurate all the time - regardless of leap years or how close to the birthdate.

Best of all - no function.