Joe Celko's Thinking in Sets: Auxiliary, Temporal, and Virtual Tables in SQL

9.5. Calendar Tables

Calendar tables are necessary because the current calendar is so irregular that you cannot reasonably compute events. Yes, there is a 19-year cycle (the Metonic cycle, named after the fifth-century Greek astronomer, Meton) in which the days of the week will repeat and you could use this to create a self-updating view if you need to use the days of the week. But it is just as easy to have a 100-year calendar in a single short table and use it.

9.5.1. Day of Week via Tables

The classic method for computing the day of the week in the Common Era calendar is a bit complicated. Here is the algorithm:

1. Take the last two digits of the year. In our example, this is 82.

2. Do integer division by 4 on the decade (two digits of the year). ...