WITH
a1 AS (SELECT 1 ID, 1 v FROM dual UNION SELECT 2, 2 v FROM dual),
a2 AS (SELECT 3 ID, 3 v FROM dual UNION SELECT 2, 2 v FROM dual),
a3 AS (SELECT 3 ID, 3 v FROM dual UNION SELECT 4, 4 v FROM dual)
SELECT COALESCE(a1.id, a2.id, a3.id) idfull,
       COALESCE(a1.v,  a2.v,  a3.v) vfull,
       CASE WHEN a1.id IS NOT NULL THEN a1.v
            WHEN a2.id is not null then a2.v
            WHEN a3.id is not null then a3.v
       end vfull1,
       a1.id, a2.v,
       a2.id, a2.v,
       a3.id, a2.v
  FROM
a1
FULL JOIN a2 ON a1.id = a2.id AND a1.v = a2.v
FULL JOIN a3 ON (a3.id, a3.v) IN ((a1.id, a1.v), (a2.id, a2.v))