Non-Clustered Index on a Clustered Index column improves performance?

Question

In SQL Server 2005, the query analyzer has told me many times to create a non-clustered index on a primary ID column of a table which already has a clustered index. After follo

Answer 1

I'd guess it would be faster in cases where you don't need the full row data, for example if you're just checking if a row with a given ID does exist. Then a clustered index would be rather huge while a small "one column" index would be much slimmer.