An index on a dual-valued column isn't likely to be of much use, unless one of the values occurs significantly less often than the other, and that's the value you search for in your query.

Here are some things that spring to mind that you could try. You'll need to test thoroughly, because even if one of these things improves the performance of the query in question, it might make things worse elsewhere.

* Make sure you're rebuilding your clustered index regularly. This will keep wasted space to a minimum and therefore reduce the IO needed for a clustered index scan

* Review the design of your table so that, for example, "On" and "Off" are stored as char(3) instead of varchar(20). This should mean that more rows can fit on each page, which will also reduce IO

* Consider creating an indexed view that includes the columns you need for your query (once you find out what those columns are)

* Consider creating a covering index consisting of only the columns you need for your query

John