Tunning Select and Where statements

Given the following statement :-

SELECT name FROM people WHERE age = 21;

Why would an index on 'age' in WHERE clause result in a slower query than having no index.
Why would an index on both 'name' and 'age' result in a faster query.

Thanks for any Help

Ming. Received on Tue Sep 28 1999 - 04:55:41 CDT