type中的multset union/distinct

DECLARE
TYPE nested_typ IS TABLE OF NUMBER;
nt1 nested_typ := nested_typ(1,2,3);
nt2 nested_typ := nested_typ(3,2,1);
nt3 nested_typ := nested_typ(2,3,1,3);
nt4 nested_typ := nested_typ(1,2,4);
answer nested_typ;
-- The results might be in a different order than you expect.
-- Remember, you should not rely on the order of elements in nested tables.
PROCEDURE print_nested_table(the_nt nested_typ) IS
output VARCHAR2(128);
BEGIN
IF the_nt IS NULL THEN
DBMS_OUTPUT.PUT_LINE('Results: ');
RETURN;
END IF;
IF the_nt.COUNT = 0 THEN
DBMS_OUTPUT.PUT_LINE('Results: empty set');
RETURN;
END IF;
FOR i IN the_nt.FIRST .. the_nt.LAST
LOOP
output := output || the_nt(i) || ' ';
END LOOP;
DBMS_OUTPUT.PUT_LINE('Results: ' || output);
END;
BEGIN
answer := nt1 MULTISET UNION nt4; -- (1,2,3,1,2,4)
print_nested_table(answer);
answer := nt1 MULTISET UNION nt3; -- (1,2,3,2,3,1,3)
print_nested_table(answer);
answer := nt1 MULTISET UNION DISTINCT nt3; -- (1,2,3)
print_nested_table(answer);
answer := nt2 MULTISET INTERSECT nt3; -- (3,2,1)
print_nested_table(answer);
answer := nt2 MULTISET INTERSECT DISTINCT nt3; -- (3,2,1)
print_nested_table(answer);
answer := SET(nt3); -- (2,3,1) ---不重复的
print_nested_table(answer);
answer := nt3 MULTISET EXCEPT nt2; -- (3)
print_nested_table(answer);
answer := nt3 MULTISET EXCEPT DISTINCT nt2; -- ()
print_nested_table(answer);
END;