Sql multiple max value in different dimensions - mysql

Question

I am trying to find a max number of the value but the thing is my code choose only max value even though values are equal so how can I find max value and if there are same make a two rows
Here is the example:
(Ps; data is fake just for example question please let me if something is wrong)
select class.name as className,
school.schoolName as schoolName,
count(school.quantity) as totalNumber from class
join School on school.schoolName = class.schoolName
group by classname, schoolName
order by schoolName
and result is:
className | SchoolNAme | TotalNum
-----------|------------|----------
Math | A | 9
Bio | A | 2
History | A | 7
Music | A | 9
Math | B | 22
English | B | 8
Music | B | 1
History | B | 2
Geo | B | 2
Bio | B | 3
Math | C | 15
Geo | C | 2
and I found each school max number like this:
select ClassName,
SchoolName,
max(totalNumber) as Total
from
(
select class.name as className,
school.schoolName as schoolName,
count(school.quantity) as totalNumber from class
join School on school.schoolName = class.schoolName
group by classname, schoolName
order by schoolName
) t1
group by schoolName
and this is the result I have:
className | SchoolNAme | Total
-----------|------------|----------
Math | A | 9
Math | B | 22
Math | C | 15
but the problem I have as we can see two total number is 9 for school A
so how can I show all max number if they are equal.
this is what I want;
className | SchoolNAme | Total
-----------|------------|----------
Math | A | 9
Bio | A | 9
Math | B | 22
Math | C | 15
Thanks

Answer 1

Max will show 1 row per group, as you are grouping by school name and there are 3 schools you will get 3 groups and therefore the 3 rows returned.
School A class Bio appears from your data to have only 2 rows (count counts the rows per group) so Bio A 9 will never be returned, so the result wanted will never be obtainable. I guess you really expect Music A 9 instead along with Math A 9.
The School table is actually redundant in this case (based upon interpretation of the join and the ensuing data i.e. count is count the number of joined rows and thus the number of class rows).
As such i believe the following produces the results that you are after :-
WITH
cte1 AS
(SELECT name,schoolName, count() AS cnt FROM class
GROUP BY name,schoolName),
cte2 AS
(SELECT name, schoolName, max(cnt) AS m FROM cte1
GROUP BY schoolname)
-- SELECT * FROM cte2
SELECT cte1.name, cte1.schoolName, cte1.cnt FROM cte1
WHERE cte1.cnt = (SELECT m FROM cte2 WHERE cte2.schoolname = cte1.schoolname)
ORDER BY schoolName, name
;
The above was tested using the following :-
DROP TABLE IF EXISTS school;
DROP TABLE IF EXISTS class;
CREATE TABLE IF NOT EXISTS school (schoolName TEXT, quantity INTEGER);
CREATE TABLE IF NOT EXISTS class (name TEXT, schoolName);
INSERT INTO school VALUES ('A',1),('B',1),('C',1);
INSERT INTO class VALUES
('Math','A'),('Math','A'),('Math','A'),('Math','A'),('Math','A'),('Math','A'),('Math','A'),('Math','A'),('Math','A'),
('Bio','A'),('Bio','A'),
('History','A'),('History','A'),('History','A'),('History','A'),('History','A'),('History','A'),('History','A'),
('Music','A'),('Music','A'),('Music','A'),('Music','A'),('Music','A'),('Music','A'),('Music','A'),('Music','A'),('Music','A'),
('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),('Math','B'),
('English','B'),('English','B'),('English','B'),('English','B'),('English','B'),('English','B'),('English','B'),('English','B'),
('Music','B'),
('History','B'),('History','B'),
('Geo','B'),('Geo','B'),
('Bio','B'),('Bio','B'),('Bio','B'),
('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),('Math','C'),
('Geo','C'),('Geo','C')
;
select class.name as className, school.schoolName as schoolName, count() as totalNumber from class
join School on school.schoolName = class.schoolName
group by classname, school.schoolName
order by schoolName, totalNumber DESC
;
select ClassName, SchoolName, max(totalNumber) as Total
from
(
select class.name as className, school.schoolName as schoolName, count(school.quantity) as totalNumber from class
join School on school.schoolName = class.schoolName
group by classname,school.schoolname
order by schoolName
)
group by schoolName;
WITH
cte1 AS
(SELECT name,schoolName, count() AS cnt FROM class
GROUP BY name,schoolName),
cte2 AS
(SELECT name, schoolName, max(cnt) AS m FROM cte1
GROUP BY schoolname)
-- SELECT * FROM cte2
SELECT cte1.name, cte1.schoolName, cte1.cnt FROM cte1
WHERE cte1.cnt = (SELECT m FROM cte2 WHERE cte2.schoolname = cte1.schoolname)
ORDER BY schoolName, name
;
Results
First Query
The first query is your query, the results match the results in the question :-
Second Query
Again this matches the unwanted/wrong results from your question :-
Third Query
This I believe matches what you require :-