[chaz]

A common alternative to this for data warehouses and reporting platforms is to construct a date table in advance, with every date enumerated from, say, 1990 through 2050. Every row represents one day, with day of week, weeks, months, and quarters as columns all set in advance. This also allows for named weeks and months, for example 2013Q3, 2013W30, and 2013M07. I also tend to put in the starting and end dates for the week in each row. It's also useful for left joining against if you need a report to show a 0 for days where you have no data.

[jacques_chester]

For the interest of persons here assembled, this is known as "dimensional modelling". Done properly, it makes querying tremendously simpler and more powerful for end users.