How to execute UNION without sorting? (SQL)

Question

UNION joins two results and remove duplicates, while UNION ALL does not remove duplicates.
UNION also sort the final output.

W

Answer 1

SELECT *, 1 AS sort_order
  FROM table1
 EXCEPT 
SELECT *, 1 AS sort_order
  FROM table2
UNION
SELECT *, 1 AS sort_order
  FROM table1
 INTERSECT 
SELECT *, 1 AS sort_order
  FROM table2
UNION
SELECT *, 2 AS sort_order
  FROM table2
 EXCEPT 
SELECT *, 2 AS sort_order
  FROM table1
ORDER BY sort_order;

But the real answer is: other than the ORDER BY clause, the sort order will by arbitrary and not guaranteed.