SQL JOIN或UNION还是什么？

Question

我有3个表名为A，B和C.表A有列a。表B列a，b。表C列a，c。这些表中包含类似下面的数据：

我想从A，B，C中的所有数据，其中a = 1

我的期望输出应该如下：

但我从SSMS得到的结果如下：

我应该如何重构我的SQL来获得我想要的输出？

例如我不想在列中重复的值

Answer 1

您需要加入这些值，但不仅在a值上，而且在该位置上。 SQL表格表示无序集合。我将假定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;