不同表中的总和之和

Question

我有SQL查询的问题。
我有桌子A：

productA priceA  
P1        18  
P2        35  
P1        22  
P2        19  

还有tableB：

productB priceB  
P1        3  
P2        15  
P1        80  
P2        96  

我希望结果是2个表中的两个产品的总和。

product price  
P1       123  
P2       165  

我想总结两张桌子的总和。
我正在尝试这个查询，但这是错误的。

SELECT productA, 
     (SELECT SUM(priceA) FROM tableA GROUP BY productA), 
     (SELECT SUM(priceB) FROM tableB GROUP BY productB)
FROM tableA, tableB
WHERE productA = productB
GROUP BY productA

请帮我。

Answer 1

您可以使用union来合并表，并对结果进行group by ：

select  product
,       sum(price)
from    (
        select  productA as product
        ,       priceA as price
        from    TableA
        union all
        select  productB
        ,       priceB
        from    TableB
        ) as SubQueryAlias
group by
        product

Answer 2

这实际上是总和的总和：

select
    product,
    sum(price)
from (
    select productA as product, sum(priceA) as price from tableA group by 1
    union all
    select productB, sum(priceB) from tableB group by 1
) 
group by 1

Answer 3

因为连接似乎是解决此问题的一种自然方式，所以这是一个使用join而不是union的解决方案。 它首先聚合子查询中的数据，然后将结果连接在一起：

select coalesce(a.productA, b.productB) as product,
       coalesce(a.PriceA, 0) + coalesce(b.PriceB, 0) as price
from (select productA, sum(PriceA) as PriceA
      from TableA
      group by productA
     ) a full outer join
     (select productB, sum(PriceB) as PriceB
      from TableB
      group by productB
     ) b
     on a.productA = b.prodctB

我正在使用full outer join ，以防表有不同的产品组。 因此，我需要在select语句中使用coalesce 。