Creating a DateTime Format Function

While it is possible to format dates using T-SQL, it is not always efficient.  Sure there are a million custom format functions available and you can even use the CONVERT function and specify a “style” but that limits you to a pre-defined set of date formats.  This is where CLR integration comes into play.

The Microsoft .NET Framework has powerful string formatting capabilities for its own DateTime data type.  By calling the “ToString” function of a DateTime object, you can specify a format string and get a formatted DateTime in just about any format you can imagine.  What we’ll do in this post is take a look at how to create a simple CLR function that takes a SQL Server DateTime value and a format string and returns a formatted string.

Creating the Assembly

First, create a new Visual Studio “Class Library” project.  We’ll call this one “ClrLib”.

The next thing you want to do is drop the automatically generated “Class1.cs” file from the project and replace it with a new class file named “StringUtilities.cs”.

This class will contain one method named “DateTimeFormat”  which will take as its input a SqlDateTime (the DateTime value to format) and a SqlString (the format string) and will return a SqlString (the formatted DateTime value).

StringUtilities.cs

Once you’ve compiled the ClrLib assembly, it is time to move on to installing this assembly in your SQL Server database.

Loading the Assembly in SQL Server

By default, CLR integration is disabled in SQL Server.  To enable CLR integration, execute the following code snippet:

Now that CLR integration has been enabled, it is time to load the assembly to your SQL Server database.

Once you’ve loaded the assembly and defined the function, it’s ready to use.

Summary

CLR integration is an incredibly powerful tool when used appropriately.  As you saw in this post, we were able to build a DateTime formatting function that can format a DATETIME value into almost any format you can imagine.  What’s more, the code to implement this solution is much easier to read and more elegant than most T-SQL implementations floating around the internet.  In future posts, we’ll use what we’ve covered here to explore other ways to use CLR integration to maximize SQL Server performance.  Until next time…

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SQL Server Expert, Steve Abraham, holds 8 Microsoft certifications and specializes in SQL Server and .Net Framework architecture, high availability, capacity planning, development, and performance tuning, and SQL Server Recovery.