Hugo Kornelis (9/4/2008)
Personally, I prefer SELECT * as it indicates checking for a row, not checking for a specific value or so. But that's just personal preference. From a performance viewpoint, there is absolutely no difference.
I prefer to use SELECT NULL vs. SELECT * or SELECT 'x' or SELECT 1 for my existance tests. Selecting a NULL is a bit more indicative that nothing is being selected.