Syntax options:

    INTERSECT | INTERSECT DISTINCT

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

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

                                   NOTE

       In general INTERSECT is commutative. That is, A INTERSECT B
       results in the same set of rows from B INTERSECT A. This is
       demonstrated by the examples below. However, care should be
       taken when using LIMIT TO within the different branches of
       the INTERSECT as this will make the result non deterministic
       because of possible different solution strategies employed
       by the Rdb optimizer.