SQL查询：联接union all查询的结果

我有以下SQL查询：

select SUM(Amount) Amount 
from
    (
        select Amount from IncomeSource1
        union all
        select Amount from IncomeSource2
    ) inc

现在，我需要根据不同表中的某种类型筛选此表的结果。假设连接是这样的：

select Amount 
from IncomeSource1 ic1
     left join IncomeType it on it.id = ic1.id
where it.IncomeType = 1

我在下面尝试，但没有运气，我仍然得到了所有金额的总和

select Id, SUM(Amount) Amount 
from
    (
        select Id, Amount from IncomeSource1
        union all
        select Id, Amount from IncomeSource2
    ) inc
    left join IncomeType it on it.id = inc.id and it.IncomeType = 1

---

如何实现此目的？

如果我理解正确，请从

选择中删除
id
：

select SUM(Amount) as Amount
from (select Id, Amount from IncomeSource1
      union all
      select Id, Amount from IncomeSource2
     ) inc left join
     IncomeType it
     on it.id = inc.id and it.IncomeType = 1;

语句中的问题是有一个
左联接
，它将始终包括联接左侧的所有行

如果您在…

上执行左联接B，则将始终返回A中的所有行。如果A和B之间不匹配，则B的列值将为NULL

相反，您需要的是一个

内部联接

，它将只返回在…上的

内部联接B中a和B之间存在匹配的行。在您的情况下，这将只返回A中满足B中相应收入类型的行


如果要按Id对总和进行分组：

select Id, SUM(Amount) Amount 
from
    (
        select Id, Amount from IncomeSource1
        union all
        select Id, Amount from IncomeSource2
    ) inc
    inner join IncomeType it on it.id = inc.id and it.IncomeType = 1
group by id;


如果您想要所有Id的总和：

select SUM(Amount) Amount 
from
    (
        select Id, Amount from IncomeSource1
        union all
        select Id, Amount from IncomeSource2
    ) inc
    inner join IncomeType it on it.id = inc.id and it.IncomeType = 1;