如何連接表格而不是重複數據

Question

我是新來的，因爲我在學習SQL，而且遇到了一個我無法解決的問題。請幫幫我。 我有兩個表結果和收入與數據，看到表的截圖。 https://www.box.com/s/5c1ah5qi9jg5ty499wvs

我想加入這些表格，但由於carthesian產品的某些數據被添加了兩次。這裏是我的代碼：

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 

有什麼建議嗎？提前致謝。

G.

Answer 1

我想你想要的是一個full outer join，而不是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，你可能想要做的兩個表之間的union，然後彙總，如：

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 

即使每個表中有給定點/ dat的多行，該版本也能正常工作e組合。