Gabung penuh beberapa tabel pada kolom yang sama

Ada beberapa cara, tapi menurut saya berikut ini yang paling populer:

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;

Jika Anda memiliki tabel terpisah dari semua k nilai, Anda dapat menggunakannya sebagai ganti allk subkueri.

Cara yang lebih mudah untuk menulis full outer join kueri adalah menggunakan 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);

Dan metode ketiga adalah union all /group by metode:

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;