mysqljoinmaxmaxdate

MYSQL Select MAX Date in a 3 table join grouped by the ID in the 1st table


I have three tables, one called BookingDetails that stores the client info. 140,000 records

CustomerRef Name Expiry
1 John 2023-12-17
2 Sarah 2024-06-17
3 Fred 2024-09-10
4 Bill 2022-03-11

The second called BookingRequest that contains the requests that client has made. 83,000 records

ID CustomerRef
1 1
2 1
3 2
4 3
5 3
83000 4

and the third called RequestLog that stores the request status of each Booking Request. 110,000 records

ID RequestID DateAdded Status
1 1 2023-08-17 Refused
2 1 2023-08-18 Pending
3 2 2023-08-19 Booked
4 3 2023-09-14 Pending
5 4 2023-09-19 Pending
6 5 2023-10-17 Refused
110000 83000 2023-10-18 Pending

I need to find all current clients that haven't booked, so I am looking to perform a join to return only the MAX(Status) grouped by Client where the expiry date is greater than now. The problem I have is that a client can have multiple booking requests. The query I have done works correctly if a client only has one request, but if a client has a request where the the lastest Status is 'booked' but then has another request where the latest status is 'pending' it is appearing in the list. I need to ONLY show clients where the latest status of ANY of their requests is anything apart from 'booked'.

SELECT BookingDetails.CustomerRef, BookingDetails.Name, BookingDetails.Expiry, b.Status AS Holidaystatus FROM BookingDetails JOIN BookingRequest ON BookingRequest.CustomerRef= BookingDetails.CustomerRef INNER JOIN RequestLog a ON a.RequestID=BookingRequest.ID JOIN (SELECT MAX(DateAdded) maxdate, RequestID FROM RequestLog GROUP BY RequestID) AS b ON a.RequestID=b.RequestID AND a.DateAdded=b.maxdate WHERE a.Status != 'Booked' AND DATE(BookingDetails.Expiry) > CURDATE() GROUP BY  BookingDetails.CustomerRef

What I want to see is

CustomerRef Name Expiry Status
2 Sarah 2024-06-17 Pending
3 Fred 2024-09-10 Refused

What I am seeing is

CustomerRef Name Expiry Status
1 John 2023-12-17 Pending
2 Sarah 2024-06-17 Pending
3 Fred 2024-09-10 Refused

Solution

  • You can use a subquery to identify the latest status for each client's requests and then filter based on that result.

    SELECT
        BD.CustomerRef,
        BD.Name,
        BD.Expiry,
        RL.Status AS HolidayStatus
    FROM
        BookingDetails BD
    LEFT JOIN (
        SELECT
            BR.CustomerRef,
            MAX(RL.DateAdded) AS MaxDate
        FROM
            BookingRequest BR
        INNER JOIN RequestLog RL ON BR.ID = RL.RequestID
        GROUP BY
            BR.CustomerRef
    ) LatestStatus ON BD.CustomerRef = LatestStatus.CustomerRef
    LEFT JOIN BookingRequest BR ON BD.CustomerRef = BR.CustomerRef
    LEFT JOIN RequestLog RL ON BR.ID = RL.RequestID
    WHERE
        LatestStatus.MaxDate IS NULL OR LatestStatus.MaxDate = RL.DateAdded
        AND DATE(BD.Expiry) > CURDATE()
        AND (RL.Status IS NULL OR RL.Status != 'Booked');
    

    This query first creates a subquery (LatestStatus) to find the maximum date added for each customer's requests. Then, it joins the BookingDetails table with the LatestStatus subquery and the other necessary tables.