PostgreSQL：如何将两列相乘并在同一查询中显示结果？

Question

我有一个查询，它的select语句是这样的：

select Greatest(p.price,0) as newprice, sum(q.qty) as qty
from ....

它给了我：

     newprice qty
      10      1
      0       1
      100     2
      1       2

我想将newprice与qty相乘得到：

    newprice  qty   result
      10      1      10
      0       1      0
      100     2     200
      1       2      2

当我尝试做select Greatest(p.price,0) as newprice, sum(q.qty) as qty, newprice * qty它说

ERROR: column "newprice" does not exist

我真的不需要这个额外的专栏。

我真正想要的是：SUM(Greatest(p.price,0) * SUM(q.qty))应该给212的价值，但它说ERROR: aggregate function calls cannot be nested

基本上我只需要将两列相乘并对结果求和。我知道我可以使用类似于here所示的CTE，但我想知道是否有更简单的方法来减少代码。

Answer 1

你可以重复你写的内容：

select Greatest(p.price,0) as newprice,
       sum(q.qty) as qty,
       Greatest(p.price,0) * sum(q.qty) as result
from ...

或者，您可以将select语句包装到临时派生表（PostgreSQL: using a calculated column in the same query）

select tmp.newprice,
       tmp.qty,
       tmp.newprice * tmp.qty as result
from (
    select Greatest(p.price,0) as newprice,
           sum(q.qty) as qty
    from ...
) as tmp

Answer 2

查询应该是这样的：

select *, newprice*qty from
(
    select Greatest(p.price,0) as newprice, sum(q.qty) as qty
    from ....
) T

要么

select Greatest(p.price,0) as newprice, sum(q.qty) as qty, Greatest(p.price,0)*sum(q.qty) as result
from ....

更新：

你在查询中使用group by（我推测是因为聚合）并且为了找到sum（newprice * qty），你需要一个子选择：

select sum(newprice*qty) from
(
    select Greatest(p.price,0) as newprice, sum(q.qty) as qty
    from ....
) T

Answer 3

试试这个：

select sum(price*qty) as result
from yourtable;