Great question. I got it wrong, but at least I learned that the two options, though ostensibly only slightly different from each other, have very different results. I need to study the NULL bitmap in more detail.
Thanks,
webrunner
-------------------
A SQL query walks into a bar and sees two tables. He walks up to them and asks, "Can I join you?"
Ref.: http://tkyte.blogspot.com/2009/02/sql-joke.html