Question

我想选择我所有最便宜的玩具，共计10.0美元：

也就是说，我想做一些看起来像这样的事情：

select * from toy where sum(price) < 10.0 order by price;

什么是正确的SQL？

为了更清楚，我将添加一个例子。假设我的表中有这些项目：

       name       | price
------------------+-------
car               |     1
boat              |     2
telephone         |     8
gold bar          |    50

我的结果是：1辆车和1艘船。

总价3美元。我无法选择电话，因为它的金额为13美元，而且大于10美元。

任何想法？

Answer 1

尝试：

SELECT a.name, max(a.price) price 
FROM Toy a
JOIN Toy b
  on a.price > b.price or (a.price=b.price and a.name>=b.name)
GROUP BY a.name
HAVING SUM(b.price) <= 10.0
order by 2

SQLFiddle here。

Answer 2

SQL Fiddle

select name, price, total
from (
    select
        name, price,
        sum(price) over(
            order by price
            rows between unbounded preceding and current row
        ) total
    from toy
) s
where total <= 10
order by price

请注意，虽然between unbounded preceding and current row是默认框架，但默认模式为range。因此，必须至少声明rows unbounded preceding，因为当前行是帧结束默认值。

Answer 3

这是使用递归CTE的实现。还有其他解决方案，您可以谷歌“运行总计”。

WITH RECURSIVE CTE_RN  AS 
(
    SELECT *, ROW_NUMBER() OVER (ORDER BY Price) RN FROM Toys
)
, CTE_Rec AS
(
    SELECT name, price, rn FROM CTE_RN WHERE RN = 1
    UNION ALL
    SELECt r.name, a.price + r.price as price, r.rn FROM CTE_RN r
    INNER JOIN CTE_Rec a on a.RN + 1 = r.RN
    where a.price+r.price <= 10
 )
SELECT name, price as total_price FROM CTE_Rec

SQLFiddle Demo

PS：它在很大程度上取决于RDBMS，因此在开始时包含该信息非常重要。

如何通过总和限制选择？

3 个答案: