This is one of the best QOTDs I have ever seen here. I had to really think this through to get it right. I ALMOST just checked #1 out of first impulse but figured it couldn't be that easy, especially once I saw the RIGHT JOIN answers. Wondering what would cause a DBA to make it that tough, I read the first query very carefully and realized that that the inner join would happen first and wouldn't happen the same on the query #1. So I ruled that out and #2 was easy to rule out. #3 screwed up the WHERE clause, so it had to be #4. A lot of work for first thing in the morning, but a good set of work as in my experience developers use nested joins not intentionally but by accident, as they are not up to speed on ANSI joins and are used to doing joins in the WHERE clause. And when they move to ANSI they sometimes do things like this. So very practical for real life troubleshooting.