sql - 查询在 postgresql 中没有相应地工作

Question

Select sum(num) as num, sum(numbr) as numbr
from
(
    (Select 0 as num)
    union all
    (Select 1 as num)
) t, 
(
    (Select 2 as numbr)
    union all
    (Select 3 as numbr)
) t1

给出结果:

num numbr
2   10

但正确的结果应该是

num numbr
1   5

Answer 1

您正在计算一个包含 0 和 1 的表格与一个包含 2 和 3 的表格的叉积。尝试删除总和:

Select num, numbr as numbr from 
(
(Select 0 as num)
union all
(Select 1 as num))t, 
((Select 2 as numbr)
union all
(Select 3 as numbr)
)t1

这给你:

0;2
0;3
1;2
1;3

这将正确地求和为 2 和 10。