A stored procedure used in our production environment recently became so slow it cause the calling web service to begin timing out. When running the stored procedure in Query Analyzer it took nearly 3 minutes to complete.

The stored procedure itself does little more than create a small bit of dynamic SQL which calls a view with a where clause at the end.

At first the thought was that the query used within the view needed to be optimized. The query is quite long and therefore easy to jump to this conclusion.

Fortunately, after bringing the issue to the attention of a coworker they asked "is there a where clause, and if so, is there an index on the column(s) in it?" I had no idea and quickly said as much. A quick check on the table/column utilized in the where clause indicated indeed there was no index.

Before adding the index, and after admitting I am no SQL wiz, I checked the internet for info on the difference between clustered and non-clustered indexes. I found the following site quite helpful OdeToCode. After adding the non-clustered index on the column, the query that used to take nearly 3 minutes now takes 10 seconds! Ah, if only I'd thought to do this ahead of time!