Vaibhav Difference between amount <> null and amount is not null

[compo guy]

  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).
>