Sql 查找两个选择的结果的差异

我有两张桌子：

table_1:  
A | B | C  
z | x | 12  
z | c | 13  
z | c | 10  
a | s | 14  
a | d | 11  

table_2:  
A | B | C  
z | c | 10  
z | x | 15  
z | x | 11  
a | d | 14  
a | s | 12  

我想：
-将表格按A和B分组
-求出AB的C和的差

我从以下几点开始：

SELECT A, B, SUM(C) from table_1 GROUP BY A, B;  
SELECT A, B, SUM(C) from table_2 GROUP BY A, B;

但我不知道如何通过添加相等的附加列来连接它们 至表1.总和（C）-表2.总和（C）

预期结果如下：

A | B | sum1 | sum2 | diff  
z | x | 12   | 26   | -14 
z | c | 23   | 10   | 13
a | s | 14   | 12   | 2
a | d | 11   | 14   | -3

将联接与子查询一起使用

select X.A,X.B, sum1, sum2, sum1-sum2 as diff from 
(
SELECT A, B, SUM(C) sum1
from table_1 GROUP BY A, B  
)X inner join
(
SELECT A, B, SUM(C) sum2
from table_2 GROUP BY A, B
)Y on X.A=Y.A and X.B=Y.B

---

当两个表中的组不相同时，您希望发生什么<代码>内部联接可能很危险，因为组将消失

如果要保留所有组，则有一种方法是

union all

/

groupby

：

select a, b, sum(c1) as sum1, sum(c2) as sum2,
       (sum(c2) - sum(c1)) as diff
from ((select a, b, c as c1, 0 as c2
       from table_1
      ) union all
      (select a, b, 0 as c1, c as c2
       from table_2
      )
     ) t
group by a, b

---

同时指定预期结果（具有该表数据）