get data under two different names when use union select

Question

"SELECT accepted AS accepted1 
 FROM friends WHERE from_id = :request_from AND to_id = :request_to 
 UNION SELECT accepted AS accepted2 
 FROM friends WHERE from_id = :request_to2 AND to_id = :request_from2"

in this query i am getting all results as accepted1 even if the second part (after UNION SELECT) of the query was true. How do i get the result as a accepted2 from second part of the query?

Answer 1

This is how the UNION statement behaves. Very generally speaking, it combines the results of two queries into one. So since you're only selecting a single field in each query, there is only a single column -- a single column can only have a single name.

If you need to know which query it came from, you could add a second column and use it to know.

SELECT accepted, 'accepted1' as source
FROM friends 
WHERE from_id = :request_from 
    AND to_id = :request_to 
UNION 
SELECT accepted, 'accepted2'  
FROM friends 
WHERE from_id = :request_to2 
    AND to_id = :request_from2

Answer 2

I think you could simplify the query by doing this:

SELECT accepted, from_id AS 'from' FROM friends 
WHERE (from_id = :request_from AND to_id = :request_to) 
   OR (from_id = :request_to2  AND to_id = :request_from2)

The second field from indicates which of the parts has been used