How to get max value of a grouped counted variable in MySQL

Question

I have a MySQL table like this;

recordID| netcall    | sign | activity | netid
1       | group1     | wa1  | 1        | 20
2       | group2     | wa2  | 2        | 30
3       | group1     | wa2  | 1        | 20
4       | group2     | wa3  | 2        | 30
5       | group1     | wa1  | 1        | 40
6       | group3     | wa4  | 3        | 50
7       | group3     | wa4  | 3        | 50
8       | group1     | wa2  | 1        | 40
9       | group1     | wa1  | 1        | 40
10      | group2     | wa4  | 2        | 60

What I need from that is:

Netcall | count | activity | netid
Group1  | 3     | 1        | 40
Group2  | 2     | 2        | 30
Group3  | 2     | 3        | 50

I thought I could;

SELECT MAX(xx.mycount) AS MAXcount
  FROM (SELECT COUNT(tt.sign) AS mycount ,tt.activity
        FROM NetLog tt
       WHERE ID <> 0
       GROUP BY netcall) xx

But this only brings up the grand total not broken down by netcall. I don't see an example of this question but I'm sure there is one, I'm just asking it wrong.

Answer 1

Your example and desire output are too basic, you should try to expand so include more cases.

Right now you can get the desire output with:

SELECT `netcall`, COUNT(*) as `total`, MAX(`activity`) as `activity`
FROM t
GROUP BY `netcall`;

My guess is you can have different activities for group so you need multiples steps

• Calculate the COUNT() for GROUP BY netcall, activity I call it q
• Then see what is the MAX(total) for each netcall I call it p
• Now you reuse q as o you have all the count, so just select the one with the max count.

SQL DEMO

SELECT o.`netcall`, o.total, o.`activity`
FROM (
      SELECT `netcall`, COUNT(*) `total`, `activity`
      FROM t
      GROUP BY `netcall`, `activity`
     ) o 
JOIN (     
      SELECT `netcall`, MAX(`total`) as `total`
      FROM (
        SELECT `netcall`, COUNT(*) `total`
        FROM t
        GROUP BY `netcall`, `activity`
      ) q  
      GROUP BY `netcall`
     ) p
  ON o.`netcall` = p.`netcall`
 AND o.`total` = p.`total`

With MySQL v8+ you can use cte and window function to simplify a little bit

with group_count as (
  SELECT `netcall`, COUNT(*) as total, `activity`        
  FROM t
  GROUP BY `netcall`, `activity`
), group_sort as (
  SELECT `netcall`, total, `activity`, 
          RANK() OVER (PARTITION BY `netcall`, `activity` ORDER BY total DESC) as rnk
  FROM group_count
)  
SELECT *
FROM group_sort
WHERE rnk = 1

Answer 2

This question is asked (and answered) every day on SO; it even has its own chapter in the MySQL manual, but anyway...

SELECT a.netcall
     , b.total
     , a.activity
  FROM netlog a
  JOIN
     ( SELECT netcall 
            , MAX(record_id) record_id
            , COUNT(*) total
         FROM netlog 
        GROUP 
           BY netcall 
    ) b
   ON b.netcall = a.netcall
  AND b.record_id = a.record_id

Answer 3

    SELECT k.netcall, k.netID,  MAX(k.logins) highest, 
AVG(k.logins) average, netDate, activity
                          FROM
                            (SELECT netID, netcall, COUNT(*) logins, DATE(`logdate`) as netDate, activity
                               FROM NetLog
                              WHERE netID <> 0 AND status = 1
                                AND netcall <> '0' AND netcall <> ''
                              GROUP BY netcall, netID) k
                            GROUP BY netcall  
                            ORDER BY highest DESC 

Resulted in:

Net Call    Highest Average Net ID  Sub Net Of...   ICS
214   309   Map Date    Activity
MESN    65  41.5294 339     214     309 MAP 2017-09-03  MESN
W0KCN   34  14.9597 1       214     309 MAP 2016-03-15  KCNARES Weekly 2m Voice Net
W0ERH   31  31.0000 883     214     309 MAP 2018-10-12  Johnson Co. Radio Amateurs Club Meeting Net
KCABARC 29  22.3333 57      214     309 MAP 2016-10-10  KCA Blind Amateurs Weekly 2m Voice Net

....