I have a rather huge query that is needed in several stored procedures, and I’d like to shift it into a UDF to make it easier to maintain (A view won’t work, this takes in a bunch of parameters), however everyone I’ve ever talked to has told me that UDF’s are incredibly slow.
While I don’t know what exactly makes them slow, I’m will to guess that they are, but seeing as I’m not using this UDF within a join, but instead to return a table variable, I think it wouldn’t be that bad.
So I guess the question is, should I avoid UDFs at all cost? Can anyone point to concrete evidence stating that they are slower?
Scalar UDFs are very slow, inline UDFs are in fact macros, as such they are very fast:
A few articles:
Reuse Your Code with Table-Valued UDFs
Many nested inline UDFs are very fast
More links on slowness of scalar UDFs:
SQL Server Performance patterns of a UDF with datetime parameters
Not all UDFs are bad for performance