SQL query MAX(SUM(..)) [closed] - sql

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Table Structure:
Article(
model int(key),
year int(key),
author varchar(key),
num int)
num: number of articles wrote during the year
Find all the authors that each one of them in one year atleast wrote maximal number of articles (relative to all the other authors)
I tried:
SELECT author FROM Article,
(SELECT year,max(sumnum) s FROM
(SELECT year,author,SUM(num) sumnum FROM Article GROUP BY year,author)
GROUP BY year) AS B WHERE Article.year=B.year and Article.num=B.s;
Is this the right answer?
Thanks.

Answer 1

You might want to try a self-JOIN to get what you are looking for:
SELECT Main.author
FROM Article AS Main
INNER JOIN (
SELECT year
,author
,SUM(num) AS sumnum
FROM Article
GROUP BY year
,author
) AS SumMain
ON SumMain.year = Main.year
AND SumMain.author = Main.author
GROUP BY Main.author
HAVING SUM(Main.num) = MAX(SumMain.sumnum)
;
This would guarantee (as it is ANSI) you are getting the MAX of the SUMmed nums and only bringing back results for what you need. Keep in mind I only JOINed on those two fields because of the information provided ... if you have a unique ID you can JOIN on, or you require more specificity to get a 1-to-1 match, adjust accordingly.
Depending on what DBMS you are using, it can be simplified one of two ways:
SELECT author
FROM (
SELECT year
,author
,SUM(num) AS sumnum
FROM Article
GROUP BY year
,author
HAVING SUM(num) = MAX(sumnum)
) AS Main
;
Some DBMSes allow you to do multiple aggregate functions, and this could work there.
If your DBMS allows you to do OLAP functions, you can do something like this:
SELECT author
FROM (
SELECT year
,author
,SUM(num) AS sumnum
FROM Article
GROUP BY year
,author
) AS Main
QUALIFY (
ROW_NUMBER() OVER (
PARTITION BY author
,year
ORDER BY sumnum DESC
) = 1
)
;
Which would limit the result set to only the highest sumnum, although you may need more parameters to handle things if you wanted the year to be involved (you are GROUPing by it, only reason I bring it up).
Hope this helps!

Answer 2

You mention for homework and a valid attempt, however incorrect.
This is under a premise (unclear since no sample data) that the model column is like an auto-increment, and there is only going to be one entry per author per year and never multiple records for the same author within the same year. Ex:
model year author num
===== ==== ====== ===
1 2013 A 15
2 2013 C 18
3 2013 X 17
4 2014 A 16
5 2014 B 12
6 2014 C 16
7 2014 X 18
8 2014 Y 18
So the result expected is highest article count in 2013 = 18 and would only return author "C". In 2014, highest article count is 18 and would return authors "X" and "Y"
First, get a query of what was the maximum number of articles written...
select
year,
max( num ) as ArticlesPerYear
from
Article
GROUP BY
year
This would give you one record per year, and the maximum number of articles published... so if you had data for years 2010-2014, you would at MOST have 5 records returned. Now, it is as simple as joining this to the original table that had the matching year and articles
select
A2.*
from
( select
year,
max( num ) as ArticlesPerYear
from
Article
GROUP BY
year ) PreQuery
JOIN Article A2
on PreQuery.Year = A2.Year
AND PreQuery.ArticlesPerYear = A2.num

Answer 3

I suggest a CTE
WITH maxyear AS
(SELECT year, max(num) AS max_articles
FROM article
GROUP BY year)
SELECT DISTINCT author
FROM article a
JOIN maxyear m
ON a.year=m.year AND a.num=m.max_articles;
and compare that in performance to a partition, which is another way
SELECT DISTINCT author FROM
(SELECT author, rank() AS r
OVER (PARTITION BY year ORDER BY num DESC)
FROM article) AS subq
WHERE r = 1;
I think some RDBMS will let you put HAVING rank()=1 on the subquery and then you don't need to nest queries.