sql - 如何连接表而不重复数据

Question

我是新来的，因为我正在学习 SQL，但遇到了一个我无法解决的问题。请帮我。我有两个表格结果和收入数据，请参阅表格的屏幕截图。 https://www.box.com/s/5c1ah5qi9jg5ty499wvs

我想加入这些表，但由于 carthesian 产品，一些数据被添加了两次。这是我的代码：

select o.point, o.date, sum(out), sum(inc) from outcome o left join income i on o.point=i.point and o.date=i.date 
group by o.point, o.date
union
select i.point, i.date, sum(out), sum(inc) from income i left join outcome o on o.point=i.point and o.date=i.date
group by i.point, i.date

有什么建议吗？提前致谢。

G。

Answer 1

我认为你想要的是 afull outer join而不是 a union：

select coalesce(o.point, i.point) as point,
       coalesce(o.date, i.date) as date,
       sum(out), sum(inc)
from outcome o full outer join
     income i
     on o.point=i.point and o.date=i.date 
group by coalesce(o.point, i.point) , coalesce(o.date, i.date) 

或者，您可能希望union在两个表之间执行 a，然后进行聚合，如下所示：

select point, date, sum(out), sum(inc)
from ((select o.point, o.date, out, NULL as inc
       from outcome
      ) union all
      (select i.point, i.date, NULL as out, inc
       from income
      )
     ) io
group by point, date

即使每个表中针对给定的点/日期组合有多行，此版本也将正常工作。