如何在3个表中加入和求和，我需要按一个键列进行分组

Question

我正在尝试连接3个表（tableA，tableB，tableC）都有3个字段（invoice，productClass，value）.tableA和tableB在productClass字段中没有值，tableC在Value字段中没有值。所有表都具有公共值Invoice但不同的ProductClass，结果应该基于发票和ProductClass对值进行求和

create table tableA (
    Invoice varchar(100),
    ProductClass varchar(100),
    Value int
)
create table tableB (
    Invoice varchar(100),
    ProductClass varchar(100),
    Value int
)
create table tableC (
    Invoice varchar(100),
    ProductClass varchar(100),
    Value int
)

insert into tableA
values
('001','',10),
('002','',20),
('003','',30),
('004','',40)


insert into tableB
values
('001','',20),
('002','',30),
('003','',40),
('004','',50)


insert into tableC
values
('001','aaa',null),
('002','aab',null),
('003','aac',null),
('004','aad',null)



select Invoice,ProductClass,sum(Value)
from(
    select * from tableA
    union
    select * from tableB
    union
    select * from tableC
)tableD
group by Invoice,ProductClass

我希望结果能够回归

Invoice - 001,002,003,004
ProductClass - aaa,aab,aac,aad
Value - 30,50,70,90

Answer 1

你可以使用max()作为ProductClass，如果它的值有blank或nulls：

select Invoice, max(ProductClass) as ProductClass, sum(Value) as Value
from(select * from tableA
     union
     select * from tableB
     union
     select * from tableC
    )tableD
group by Invoice;