कई तरीके हैं, लेकिन मुझे लगता है कि निम्नलिखित सबसे लोकप्रिय हैं:
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;
यदि आपके पास सभी k
. की एक अलग तालिका है मान, आप इसका उपयोग allk
. के बजाय कर सकते हैं सबक्वेरी।
अपना full outer join
लिखने का एक आसान तरीका क्वेरी का उपयोग करना है 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);
और तीसरा तरीका है union all
/group by
विधि:
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;