My query is taking too long to finish for finding the pair of rows where the difference of columns value is maximum group by another column

Question

Say, I\'ve a table like this:

I want to find the pair of Centers whose Performance difference is highest for each session, like this:

I have th

Answer 1

Grouping by session and taking the group's min and max performance seems logical. The actual centers unfortunately need a subquery/join here.

select g.session as Session,
    (select min(center) from mytable
     where session = g.session and performance = g.maxim) as Center1,
    (select min(center) from mytable
     where session = g.session and performance = g.minim) as Center2,
    g.maxim - g.minim as Performance
from (select 
        t1.session,
        min(t1.performance) as minim,
        max(t1.performance) as maxim
    from mytable t1
    group by t1.session)
    as g

Ensure an index on session and performance.