MySQL预订可用性，重叠日期范围

Question

I have a table with bookings:

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

Bookings can overlap, so there can for example be 20 bookings at the same time. Now I want to do two queries:

1) Retrieve the maximum sum of quantities within a given period.

2) Retrieve the minimum sum of quantities within a given period.

I have no idea how to add the quantities of ONLY the overlapping bookings together, and not of non-overlapping bookings. Any help would be greatly appreciated.

edit: i drew a picture for clarity: http://i.imgur.com/8GDLV.png

Answer 1

1. Construct a list of all booking boundaries (ie start and end dates) which occur in the desired period:

     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. Add to that the boundary which occurs immediately before the desired period:

    -- [ 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. Make an outer join between this result and the bookings table, keeping all of the boundaries but only including a booking if it contributes to the number of simultaneous people after the boundary:

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

4. Sum the number of people at each boundary:

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

5. Find the maximum and minimum:

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

Putting it all together:

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

See it on sqlfiddle .

Answer 2

There is no field for grouping in given data structure in the question. So assuming you are grouping by ID .

1). To get maximum use 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). To get maximum min 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