Statistics are only maintained on the first column of a composite index.
Statistics are only maintained on the first column of a composite index. Because of this, SQL Server’s Query Optimizer might not make as good use of composite indexes as it could. If you suspect that a composite index is not being used as you expected it would be, you will want first to verify that the index is not being used by examining the query’s execution plan.
If you see that it is not being used, and it should be, consider adding a hint to force the index to be used, then see if using the index really helps performance. If it does, keep the hint. If it does not help performance, drop the hint and the composite index that is not being used, assuming that it is not needed by another query.