Pełne łączenie wielu tabel w tych samych kolumnach

Jest kilka sposobów, ale myślę, że najbardziej popularny jest ten:

select allk.k, t1.c1, t2.v2, t3.v3, t4.v4
from (select k from t1 union 
      select k from t2 union
      select k from t3 union
      select k from t4
     ) allk left outer join
     t1
     on allk.k = t1.k left outer join
     t2
     on allk.k = t2.k left outer join
     t3
     on allk.k = t3.k left outer join
     t4
     on allk.k = t4.k;

Jeśli masz osobną tabelę wszystkich k wartości, możesz użyć tego zamiast allk podzapytanie.

Łatwiejszy sposób na napisanie full outer join zapytanie polega na użyciu coalesce() :

SELECT COALESCE(t1.K, t2.K, t3.K, t4.K) [K], V1, V2, V3, V4
FROM @T1 t1 FULL JOIN
     @T2 t2
     ON t2.K = t1.K FULL JOIN
     @T3 t3
     ON t3.K = coalesce(t1.K, t2.K) FULL JOIN
     @T4 t4
     ON t4.K = coalesce(t1.K, t2.K, t3.k);

A trzecia metoda to union all /group by metoda:

select k, max(v1) as v1, max(v2) as v2, max(v3) as v3, max(v4) as v4
from (select k, v1, NULL as v2, NULL as v3, NULL as v4
      from t1 union all
      select k, NULL as v1, v2, NULL as v3, NULL as v4
      from t2 union all
      select k, NULL as v1, NULL as v2, v3, NULL as v4
      from t3 union all
      select k, NULL as v1, NULL as v2, NULL as v3, v4
      from t4
     ) t
group by k;