Hugo, 5+the number of your children is obviously 7... I think maybe you messed up your inner select 🙂

I think that this does illustrate a point that has not been made yet: Null as a value in SQL server is used to indicate more than one thing: the empty set, and the absence of a scalar value.

I think people often focus on the peculiarities of using Null as a scalar value (Null <> Null, intransitive comparisons) However Null makes a lot more sense when looking at the logical concept of an empty set.

What do I get when I Select Hugo's grandchildren? A set with no rows. What is the favorite color of Hugo's grandchild? Null