Datetime calculations are challenging. They often involve tricky logic. In the past three columns, I've gone into depth about datetime calculations, covering various types, including calculating the date of the first and last days of a month based on a given event datetime value, and calculating the last and next occurrences of a weekday. This month, I present techniques for calculating the date of the first and last occurrences of a weekday in a month, based on a given event date—fo...