Better way to select max values in multiple-column group? - mysql

Question

Simplified the following question I got from a coding challenge...
I have a table grades like:
year sex person mark
2000 M Mark 70
2010 F Alyssa 23
2020 M Robert 54
I want to select the people per year for both sexes that have the highest marks.
My Attempt:
SELECT
year,
MAX(CASE
WHEN sex = ‘F’ THEN person
ELSE ‘’ END) AS person_f,
MAX(CASE
WHEN sex = ‘M’ THEN person
ELSE ‘’ END) AS person_m
FROM (
SELECT
year,
sex,
person,
**mark
FROM grades
WHERE mark IN (
SELECT MAX(mark) AS mark
FROM grades
GROUP BY year, sex)
**) AS t
WHERE x = 1
GROUP BY 1
ORDER BY 1
I modified everything within the ** ** but the rest of the code was pre-populated. The code seemed right to me, but somehow only passed 2/4 test cases, and there were no tiebreaker records.
Also, I omitted the WHERE x = 1 line, but the correct solution apparently needs that. (yes, x isn't a column in any table)
Is there a more elegant/efficient way to solve this?
Can't seem to figure it out, and it's really bugging me.

Answer 1

First you need to use single quotes for Strings
The Problem of your query, is the subquery for your marks, you select a bunch of highest marks without associating them to the year, and gender
MySql allows you to IN clause with multiple columns.
SELECT
year,
MAX(CASE
WHEN sex = 'F' THEN person
ELSE '' END) AS person_f,
MAX(CASE
WHEN sex = 'M' THEN person
ELSE '' END) AS person_m
FROM (
SELECT
year,
sex,
person,
mark
FROM grades
WHERE (year,sex,mark) IN (
SELECT year, sex,MAX(mark) AS mark
FROM grades
GROUP BY year, sex)
) AS t
GROUP BY 1
ORDER BY 1
| year | person\_f | person\_m |
|-----:|:----------|:----------|
| 2000 | | Mark |
| 2010 | Alyssa | |
| 2020 | | Robert |
fiddle

Answer 2

I believe this approach incorporates the WHERE x = 1 clause as well.
SELECT
year,
MAX(CASE
WHEN sex = 'F' THEN person
ELSE '' END) AS person_f,
MAX(CASE
WHEN sex = 'M' THEN person
ELSE '' END) AS person_m
FROM (
SELECT
year,
sex,
person,
RANK() OVER (PARTITION BY year, sex ORDER BY mark DESC) AS x
FROM grades)
WHERE x = 1
GROUP BY 1
ORDER BY 1

Answer 3

You can use rank. I added info to the table so you could see what happens in different scenarios including a tie.
select year
,sex
,person
,mark
from (
select *
,rank() over(partition by year, sex order by mark desc) as rnk
from t
) t
where rnk = 1
order by year, sex
year
sex
person
mark
2000
F
Alyssa
23
2000
M
Mark
70
2000
M
Danny
70
2010
F
Alma
100
2010
M
Dudu
47
2020
F
Noga
98
2020
M
Moshe
56
Fiddle