Print every max value using three tables (mysql) - mysql

Question

I need to find the author who has written the most volumes in my database, I have three tables "VOLUMES", "AUTHOR", "WRITTEN BY". Table VOLUMES has columns like title, volume_id(primary key), year, edition_year, etc. Table AUTHOR has columns for generic infos like name, surname, id,etc and table WRITTEN BY is used to connect AUTHOR and VOLUMES, it contains the columns volume_id and author_id.
My data can contain many copies of the same volumes so I guess I need to group every copy of the same volume.
The query I have written is:
SELECT A.NAME, A.SURNAME, COUNT(V.ID) no_of_volumes
FROM VOLUMES AS V, AUTHOR AS A JOIN WRITTEN_BY W
WHERE (V.ID = W.VOLUME_ID AND A.ID = W.A_ID)
GROUP BY A.NAME, A.SURNAME
ORDER BY no_of_volumes DESC
LIMIT 1;
Now, this should print just one author, but I want it to print EVERY author that has written the same number of volumes... How do I do that?

Answer 1

If you are allowed to change the scheme slightly (use unique ID-names) than this could do the trick
select AUTHOR.NAME
, count(*) VolumeCount
from AUTHOR
inner join WRITTEN_BY using(AUTHOR_ID)
inner join VOLUME using(VOLUME_ID)
group by a.AUTHOR_ID
order by VolumeCount desc
limit 1;
x
If not than this should do the trick:
select AUTHOR.NAME
, count(*) VolumeCount
from AUTHOR
inner join WRITTEN_BY on AUTHOR_ID = AUTHOR.ID
inner join VOLUME on VOLUME_ID = VOLUME.ID
group by a.AUTHOR_ID
order by VolumeCount desc
limit 1;
Please reserve where for filtering only. Using it for foreign-key makes messy code.
(And if your table and field names are uppercase it makes sense to use lowercase keywords)

Answer 2

You must aggregate twice inside written_by: once to get the max number of volumes written and then to get the author ids who wrote the max number of volumes.
Then join to authors to get the authors details:
SELECT a.*, t.no_of_volumes
FROM author a INNER JOIN (
SELECT author_id, COUNT(*) no_of_volumes
FROM written_by
GROUP BY author_id
HAVING COUNT(*) = (
SELECT COUNT(*) no_of_volumes
FROM written_by
GROUP BY author_id
ORDER BY no_of_volumes DESC LIMIT 1
)
) t ON t.author_id = a.id
The table volumes is not needed.
For MySql 8.0+ the code can be simplified with the use of the window function RANK():
SELECT a.*, t.no_of_volumes
FROM author a INNER JOIN (
SELECT r.*
FROM (
SELECT author_id, COUNT(*) no_of_volumes,
RANK() OVER (ORDER BY COUNT(*) DESC) rnk
FROM written_by
GROUP BY author_id
) r
WHERE r.rnk = 1
) t ON t.author_id = a.id