MySQL预订可用性，重叠日期范围

Question

我有一张预订表：

• id（int）
• 数量（tinyint）
• date_start（timestamp）
• date_end（timestamp）

预订可以重叠，因此例如可以同时进行20次预订。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）在给定时间段内检索最小数量总和。

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

编辑：我为了清晰起见画了一张照片：http://i.imgur.com/8GDLV.png

Answer 1

1. 构建在所需期间内发生的所有预订边界（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. 添加到所需时间段之前的边界：

   -- [ 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. 在此结果与bookings表之间建立外部联接，保留所有边界，但仅包括预订，如果它有助于之后的同时人数边界：

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

4. 总结每个边界的人数：

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

5. 找出最大值和最小值：

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

全部放在一起：

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

在问题的给定数据结构中没有用于分组的字段。因此，假设您按ID进行分组。

1）。要充分利用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）。获得最大分钟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

See this SQLFiddle