Syntax options:

    EXCEPT | EXCEPT DISTINCT

    The EXCEPT DISTINCT operator is used to create a result table
    from the first select expression except for those row values that
    also occur in the second select expression.

    DISTINCT is the default so EXCEPT and EXCEPT DISTINCT are
    identical operations. EXCEPT conforms to the ANSI and ISO
    SQL:1999 Database Language Standard.

                                   NOTE

       EXCEPT is not commutative. That is, A EXCEPT B may result in
       a different set of rows from B EXCEPT A.