Yeah, if you have the ID's as null. But why you would do such thing in the first place? Have the ID be "serial primary key" and you'll never have null values in there ever!

Btw, that's the second optimization you learn. So you telling me that in your case, you have null values in your ID's? You should be fired trice then.

Since you're hell bent on doing tests, do one with a dozen millions rows, just ID and a varchar as columns, and in one case have the ID have nulls, and in the other case be like I said. Then see the difference when you run "select count(ID) where the_varchar_column = 'Steve'" vs "select(star_sign) bla bla" and come back to me. Image would be appreciated. Then go rewrite your DB structure and the query when you realize the performance