By using simple tuning techniques, you can make a big difference in the performance of certain queries. For example, the technique I demonstrated in "Are You in Tune?" July 2001, involved expressing in the form of a SARG any conditions in a query's WHERE clause that referenced indexed columns. A SARG is a search condition, expressed in a particular format; for details, see last month's column. Let me demonstrate how you can verify what I told you about SARGs and indexed columns. Then, let's explore ways that you can tell whether SQL Server is using an index and whether using the index is useful.