codility_task_difficulty.sql

-- write your code in PostgreSQL 9.4
SELECT r.task_id, t.name as task_name, 
    case when avg(r.score) <= 20 then 'Hard'
        when avg(r.score) > 20 and avg(score) <= 60 then 'Medium'
        when avg(r.score) > 60 then 'Easy' End As difficulty

    from reports r left join tasks t on r.task_id = t.id 
    group by r.task_id, task_name order by r.task_id