Find the max value when there are multiple groups to be considered

Question

I have already tried Get records with max value for each group of grouped SQL results answers from here. But it takes only group by one column. I need several. So I am posting the question here.

I have an dataset(usertable) as follows,

ID  Username    Status
1   John        Active
2   Mike        Active
3   Ann         Deactive
4   Leta        Active
5   Lena        Active
6   Lara        Active
7   Mitch       Active

Further I have a revenuetb table as follows which has substrings of each user.

subuser           hour          Revenue
John_01         2/26/2022 5:00     5
Mike_01         2/26/2022 7:00     8
Mike_01         2/26/2022 7:00     22
Leta_03         2/26/2022 7:00     67
Leta_07         2/26/2022 9:00     56
Mitch_07        2/26/2022 11:00    34

I need to match each subuser with main User(ex:John_01==John) in usertable and get the sum of revenue of each user as well. But if the Hour is repeated for each subuser I need to get the maximum Revenue of that each sub user.

As an example I need to get the revenue with 22 and should neglect 8.

Ex:
    Mike_01         2/26/2022 7:00     8
    Mike_01         2/26/2022 7:00     22

So final table should looks like below.

User    Total_Usage
John         5
Mike         22
Leta         123
Lena         0
Lara         0
Mitch        34

Here is my try.

SELECT u.Username
     , COALESCE(SUM(Revenue), 0) AS TOTAL_USAGE
  FROM usertable u
  LEFT JOIN revenuetb e
    ON SUBSTRING_INDEX(e.subuser, '_', 1) = u.Username
   AND e.Hour BETWEEN 'XXX' and 'XXX' 
 where u.STATUS='Active'       
 GROUP BY u.Username 
 order by u.ID
;

But this is not neglecting repeated Hours. Can someone explain how should I do this?

Limitation :cannot use window functions in my remote server.

Jon Armstrong · Accepted Answer · 2022-02-27T15:07:20.487

Just use a derived table to obtain the MAX(revenue) per (user, hour) groups.

Then SUM the results per user:

The fiddle

SELECT username, SUM(MAX_USAGE) AS TOTAL_USAGE
  FROM (
        SELECT u.Username, e.hour
             , COALESCE(MAX(Revenue), 0) AS MAX_USAGE
          FROM usertable u
          LEFT JOIN revenuetb e
            ON SUBSTRING_INDEX(e.subuser, '_', 1) = u.Username
           AND e.Hour BETWEEN xxx and yyy
         WHERE u.STATUS='Active'    
         GROUP BY u.Username, e.hour
       ) AS derived
 GROUP BY Username
;

Result:

username	TOTAL_USAGE
John	5
Lara	0
Lena	0
Leta	123
Mike	22
Mitch	34

Slight cheat in the fiddle with regard to the date/times. But the basic logic is the same.

For your initial SQL, I used MariaDB to avoid your GROUP BY error report. MariaDB still doesn't recognize the functional dependence mistake, much like the older versions of MySQL (prior to 5.7).

This is allowed with MySQL prior to 5.7 as well.

The final solution works fine in all versions as it doesn't contain the functional dependence mistake.

Find the max value when there are multiple groups to be considered

1 Answers1