Comments on: SQL Server Scalar UDFs (User Defined Functions)

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By: SQL Server Table-valued UDFs (User Defined Functions) « Arcane Code

SQL Server Table-valued UDFs (User Defined Functions) « Arcane Code — Thu, 25 Oct 2007 06:11:39 +0000

[...] SQL Server Scalar UDFs (User Defined Functions) [...]

By: Jeff Barnes

Jeff Barnes — Wed, 24 Oct 2007 12:37:46 +0000

You are definitely right about performance trade offs. I’m a big fan of using UDFs to encapsulate logic such as an ugly case statement, a series of IF conditions, or some kind of calculation. They are awesome in that context for improving readability and reuse. However, I am very cautious about using them for select operations.

At a previous job, I was tasked with resolving some ridiculous performance issues for a large report. It turned out that someone had written a nasty stored procedure using 7 or 8 UDFs as parameterized tables. After rewriting it to use derived tables, the execution time dropped from several minutes to less than 10 seconds!

This was a dramatic case, but it has always stuck with me.