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

This sounds like a job for union:

select sender as id from 
union
select receiver as id from 

Note that union will remove duplicates (use union all if you want to keep duplicates).