Question

在具有以下模式的表中给出数据：

CREATE TABLE purchases (timestamp DATETIME, quantity INT)

我想找到时间点（即行的时间戳），其中数量列中的值总和超过了某个阈值。

这是在MS SQL Server中，理想情况下我想尽可能避免使用游标。

Answer 1

SELECT timestamp, SUM(quantity)
FROM purchases
GROUP BY timestamp
HAVING SUM(quantity) > someValue

或者如果它是一个运行总和

SELECT a1.timestamp
FROM purchases a1, purchases a2 
WHERE a1.quantity >= a2.quantity or (a1.quantity=a2.quantity and a1.timestamp = a2.timestamp) 
GROUP BY a1.timestamp, a1.quantity
having SUM(a2.quantity) >= someValue
ORDER BY a1.timestamp ASC
LIMIT 1

Answer 2

您可以获得前一个值之和大于阈值的最小时间戳：

select min(timestamp)
from purchases p
where (
  select sum(x.quantity)
  from purchases x
  where x.timestamp < p.timestamp
) > @threshold

但是，这不是一个非常有效的查询，所以最好使用游标。

Answer 3

在SQL Server 2005+中，你可以试试这个：

;WITH numbered AS (
  SELECT
    timestamp,
    quantity,
    rownum = ROW_NUMBER() OVER (ORDER BY timestamp)
  FROM purchases
),
recursive AS (
  SELECT
    timestamp,
    quantity,
    rownum,
    runningsum = quantity,
    passed = CASE WHEN n.quantity < @threshold THEN 0 ELSE 1 END
  FROM numbered
  UNION ALL
  SELECT
    n.timestamp,
    n.quantity,
    n.rownum,
    runningsum = n.quantity + r.runningsum,
    passed = CASE WHEN n.quantity + r.runningsum < @threshold THEN 0 ELSE 1 END
  FROM numbered n
    INNER JOIN recursive r ON n.rownum = r.rownum + 1
)
SELECT MIN(timestamp)
FROM recursive
WHERE passed = 1

基本上，与@Guffa的解决方案相同，只使用CTE来避免三角形连接的需要。

如何找到列中所有值之和达到指定值的行？

3 个答案: