Numbers of weekdays in a date range in TSQL

Question

This is harder than it looks. I need a function that calculates the numbers of a given weekday in a date range. I don\'t want any loops or recursive SQL. There are millions

Answer 1

An alternative approach is the good old-fashioned data warehouse time dimension, where you have a table with all potential dates in it, along with any useful information you want to filter/count by:

Key       ActualDate  DayName   IsWeekday  DayNumberInYear  FinancialQuarter
20110101  1 Jan 2011  Saturday  0          1                2011 Q1
20110102  2 Jan 2011  Sunday    0          2                2011 Q1
20110103  3 Jan 2011  Monday    1          3                2011 Q1

Then just join to that table and filter, e.g.

SELECT 
  COUNT(*) 
FROM 
  date_dimension
WHERE
  ActualDate BETWEEN '1 Jan 2011' AND '3 Jan 2011' AND
  IsWeekday = 1

If you do date analysis a lot over a known range of dates, this can really speed up and simplify your queries. Whether you know your possible date ranges in advance is the limiting factor on whether this is helpful, really, but it's a useful trick to know about.