month – sqlsunday.com

The SQL Server Calendar project

I’m the type of developer that invents wheels. Yes, every wheel I design is unique in its own way, and hand-crafted for a specific purpose. And so it has also been with calendar dimensions (typically when I do data warehousing work).

This got me thinking – why not design the mother of all calendar dimensions? One that includes every conceivable calendar and property that I and others could use and re-use. One that could save me a ton of coding, and lessen the burden of having to validate it each and every time?

And that’s how I got started designing my one calendar script to rule them all.

Grouping dates without blocking operators

It’s not entirely uncommon to want to group by a computed expression in an aggregation query. The trouble is, whenever you group by a computed expression, SQL Server considers the ordering of the data to be lost, and this will turn your buttery-smooth Stream Aggregate operation into a Hash Match (aggregate) or create a corrective Sort operation, both of which are blocking.

Is there anything we can do about this? Yes, sometimes, like when those computed expressions are YEAR() and MONTH(), there is. But you should probably get your nerd on for this one.

A function to calculate recurring dates

When you’re using Microsoft Outlook, or pretty much any other personal information manager, you can create calendar appointments that are “recurring”, i.e. you can have them repeat at a defined frequency. This, however may not only apply to your project meeting appointments, but also to some database solution. I decided to give it a go at building a table value function that returns a list of dates, based on a given set of parameters.