Просто попробуйте этот код,
DECLARE
CURSOR ix IS SELECT owner , object_type,
object_name
FROM all_objects
WHERE object_type = 'TABLE' And upper(owner) = upper('demo');
BEGIN
FOR x IN ix LOOP
EXECUTE IMMEDIATE ( 'DROP ' || x.object_type || ' ' ||
x.owner||'.'||x.object_name || ' CASCADE CONSTRAINTS');
END LOOP;
END;