mysql - MySQL 预订可用性，重叠日期范围

Question

我有一张预订表：

• 标识（整数）
• 数量 (tinyint)
• date_start（时间戳）
• date_end（时间戳）

预订可以重叠，因此例如可以同时有 20 个预订。现在我想做两个查询：

1) 检索给定时间段内的最大数量总和。

2) 检索给定时间段内的最小数量总和。

我不知道如何将重叠预订的数量加在一起，而不是非重叠预订的数量。任何帮助将不胜感激。

编辑：为了清楚起见，我画了一张图片：http: //i.imgur.com/8GDLV.png

Answer 1

1. 构建在所需时间段内出现的所有预订边界（即开始和结束日期）的列表：

     SELECT date_start AS boundary
     FROM   bookings
     WHERE  date_start BETWEEN @start AND @end
   UNION
     SELECT date_end
     FROM   bookings
     WHERE  date_end BETWEEN @start AND @end
   

2. 添加到紧接在所需时间段之前出现的边界：

   -- [ from part 1 above ]
   UNION
     SELECT MAX(boundary)
     FROM (
       SELECT MAX(date_start) AS boundary
       FROM   bookings
       WHERE  date_start <= @start
     UNION ALL
       SELECT MAX(date_end)
       FROM   bookings
       WHERE  date_end <= @end
     ) t
   

3. 在此结果和表之间进行外部连接，保留所有边界，但仅包括一个预订，如果它有助于在边界之后bookings的同时人数：

   FROM bookings RIGHT JOIN (
     -- [ from part 2 above ]
   ) t ON date_start <= boundary AND boundary < date_end
   

4. 将每个边界的人数相加：

   SELECT IFNULL(SUM(quantity),0) AS simultaneous_people
   -- [ from part 3 above ]
   GROUP BY boundary
   

5. 求最大值和最小值：

   SELECT MIN(simultaneous_people),
          MAX(simultaneous_people)
   FROM (
     -- [ from part 4 above ]
   ) t
   

把它们放在一起：

SELECT MIN(simultaneous_people),
       MAX(simultaneous_people)
FROM (
  SELECT IFNULL(SUM(quantity),0) AS simultaneous_people
  FROM   bookings RIGHT JOIN (
    SELECT date_start AS boundary
    FROM   bookings
    WHERE  date_start BETWEEN @start AND @end
  UNION
    SELECT date_end
    FROM   bookings
    WHERE  date_end BETWEEN @start AND @end
  UNION
    SELECT MAX(boundary)
    FROM (
      SELECT MAX(date_start) AS boundary
      FROM   bookings
      WHERE  date_start <= @start
    UNION ALL
      SELECT MAX(date_end)
      FROM   bookings
      WHERE  date_end <= @end
    ) t
  ) t ON date_start <= boundary AND boundary < date_end
  GROUP BY boundary
) t

在sqlfiddle上查看。

Answer 2

问题中的给定数据结构中没有用于分组的字段。因此，假设您按ID.

1）。为了得到最大的利用MAX

SELECT MAX(TotalQty) FROM
(
    SELECT SUM(Quantity) AS TotalQty FROM Bookings
    WHERE date_End<='<To Date>'
    AND date_Start>='<From Date>'
    GROUP BY id
) SumQty

2）。获得最大最小值MIN

SELECT MIN(TotalQty) FROM
(
    SELECT SUM(Quantity) AS TotalQty FROM Bookings
    WHERE date_End<='<To Date>'
    AND date_Start>='<From Date>'
    GROUP BY id
) SumQty

看到这个 SQLFiddle