SQL JOIN或UNION還是什麼？

Question

我有3個表名爲A，B和C.表A有列a。表B列a，b。表C列a，c。這些表中包含類似下面的數據：

我想從A，B，C中的所有數據，其中a = 1

我的期望輸出應該如下：

但我從SSMS得到的結果如下：

我應該如何重構我的SQL來獲得我想要的輸出？

例如我不想在列中重複的值

Answer 1

您需要加入這些值，但不僅在a值上，而且在該位置上。 SQL表格表示無序集合。我將假定b和c列表示排序。

select a.a, b.b, c.c 
from (select a.*, row_number() over (order by a) as seqnum 
     from a 
    ) a full outer join 
    (select b.*, row_number() over (partition by a order by b) as seqnum 
     from b 
    ) b 
    on a.a = b.a and a.seqnum = b.seqnum full outer join 
    (select c.*, row_number() over (partition by a order by c) as seqnum 
     from c 
    ) c 
    on c.a = coalesce(a.a, b.a) and c.seqnum = coalesce(a.seqnum, b.seqnum) 
where coalesce(a.a, b.a, c.a) = 1;