mysql query unite 2 columns

Question

I have a table friends with 4 columns (id, sender, receiver, status) and I need a query that will unite (reunion, I dont know the word in english) the sender and receiver colums

Answer 1

SELECT DISTINCT a.iResult
FROM
    (SELECT sender as iResult FROM tableName
        UNION
     SELECT receiver as iResult FROM tableName) a
ORDER BY iResult ASC

Returns

2
3
6
7
8
9
10

OR

SELECT GROUP_CONCAT(b.iResult)
     (SELECT DISTINCT a.iResult
     FROM
             (SELECT sender as iResult FROM tableName
                 UNION
              SELECT receiver as iResult FROM tableName) a
         ORDER BY iResult ASC) b

returns

2,3,6,7,8,9,10