I did not mention the query performance in postings.  It was raised with the date issue especially in the where clause.  That's how I response. Unfortunately, someone raised the performance issue...

I used them in queries and the results have shown the difference.

SET STATISTICS IO ON

SET STATISTICS TIME ON

Are the STATISTICS useful in measuring the SQL performance ?

Let me know if...

I wouldn't be writing a query for what you wrote above.  If you design the algorithm properly then the UDF will be useful.  I recommend not to use the UDF in...

Have you try it ?

The where and between clauses are difficult to work with date expressions.

You can create an user defined function with four date parameters (two user-inputs and two data from a selected table)...