How to select something from JOIN? SQL - mysql

Question

I have two tables: cities and students. Each student has city_id which references a city in the citites table.
I have a join:
SELECT lastname, city, points_avg
FROM students INNER JOIN cities
ON students.city_id = cities.city_id where city LIKE 'Paris'
It works pretty well.
But then, I want to select the student with the highest score EXCLUSIVELY from Paris.
I tried this:
select lastname, points_avg from (
SELECT lastname, city, points_avg
FROM students INNER JOIN cities
ON students.city_id = cities.city_id where city LIKE 'Paris'
) AS join_name where points_avg = (select MAX(points_avg) from join_name);
But it says that current database doesnt have the table join_name
I wrote this:
select lastname, points_avg from (
SELECT lastname, city, points_avg
FROM students INNER JOIN cities
ON students.city_id = cities.city_id where city LIKE 'Paris'
) AS join_name where points_avg = (select MAX(points_avg) from (
SELECT lastname, city, points_avg
FROM students INNER JOIN cities
ON students.city_id = cities.city_id where city LIKE 'Paris'
) AS join_name_new);
And unexpectedly, it works, but it`s so stupid ahah
Could you advise me, how to get the same result without repeating join twice?

Answer 1

You can do this using a CTE, but not a subquery:
with join_name as (
select s.lastname, c.city, s.points_avg
from students s join
cities c
on s.city_id = c.city_id
where c.city like 'Paris'
)
select jn.lastname, jn.points_avg
from join_name jn
where jn.points_avg = (select max(jn2.points_avg) from join_name jn2);
If you are learning SQL, that is just the difference between a CTE and a subquery.
Also note the use of table aliases and qualified column references. They make it clearer what the query is really doing.
Also, I retained the structure of your query, but you rank() would be a more typical way to implement this logic.

Answer 2

#Cognosce, if you are learning SQL then #Gordon Linoff is correct!
However, a much simpler way to write same query without subquery and CTE would be:
select s.lastname, c.city, s.points_avg
from students s join
cities c
on s.city_id = c.city_id
where c.city like 'Paris'
Order by s.points_avg desc
Limit 1