@Andrew Yes, it does. ex:

SELECT 1 AS A FROM DUAL
UNION
SELECT 2 AS A FROM DUAL

To be more specific, I use REST API, When I try a similar script, it gives me an error:

Hmmm... What about trying this?

SELECT * FROM ( SELECT 1 AS A FROM DUAL UNION SELECT 2 AS A FROM DUAL )

Thank you very much, Tim. This one works! But it's really unobvious that I need to wrap the result with an additional SELECT to make it work.

Agreed!