sql - Oracle SUM 返回错误的摘要，其中包含从 SELECT UNION 返回的相同值

Question

我遇到了 SUM 语句的问题。

此查询返回 MY_ID = 1 和 QTY = 7

select my_id, sum(qty) qty
from
(     
  select 1 my_id ,2 qty from dual
union
  select 1 my_id, 5 qty from dual
)
group by my_id;

但是这个返回 MY_ID = 1 和 QTY = 5 而不是 QTY = 10。

select my_id, sum(qty) qty
from
(     
  select 1 my_id ,5 qty from dual
union
  select 1 my_id, 5 qty from dual
)
group by my_id;

如果两个值相同，我如何总结这两个数量？

Answer 1

使用联合所有:

select my_id, sum(qty) qty
from
(     
  select 1 my_id ,5 qty from dual
union all
  select 1 my_id, 5 qty from dual
)
group by my_id;