This query fetches the courses that are the most played (result in descending order by number of plays)
select
trackings.course as course_id,
courses.name as course_name,
count(distinct trackings.user) as nb_learners
from qwnogpy_ww21770_datasharing.core.courses_trackings trackings
left join qwnogpy_ww21770_datasharing.core.courses courses
on trackings.course = courses.id
group by 1, 2
order by nb_learners desc
course_id: ID of the coursecourse_name: Name of the coursenb_learners: Number of users who played the course