SELECt @id := ( SELECT senderid FROM mytable WHERe receiverid = @id ) AS personFROM ( SELECT @id := 5 ) varsSTRAIGHT_JOIN mytableWHERe @id IS NOT NULL

SELECt @id := ( SELECT senderid FROM mytable WHERe receiverid = @id ) AS personFROM ( SELECT @id := 5 ) varsSTRAIGHT_JOIN mytableWHERe @id IS NOT NULL