In the last episode (Sep 12), compo guy said:
> What is the difference between the following sql queries written to
> extract tuples with the field amount having non null value:
> select loan_number from loan where amount <> null (It returns
> an empty set)
> select loan_number from loan where amount is not null(It
> returns the expected result).
NULL is a special value. it can only be compared with "IS NULL" or "IS
NOT NULL". "= NULL" and "<> NULL" always return false.