INSERT-ing to a table if the the data does not already exits - how do indexes peform in this scenario?
A clustered index IS the table - so if the rows you are adding are already ordered there is not much work to do. A non-clustered index is an extra structure that you will have to maintain - so Inserts, Updates &amp; Deletes will all have an overhead, the more indexes the higher the overhead. Generally, there are some selects for every table (otherwise what is the point of storing the data?), The balance between the improved SELECT performance versus the maintenance overhead can really only be determined for your particular workload - so measure twice &amp; cut once!