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