Here's my code:
select yr,count(*) from movie
join casting on casting.movieid=movie.id
join actor on casting.actorid = actor.id
where actor.name = 'John Travolta'
group by yr
Which were the busiest years for 'John Travolta'. Show the number of movies he made for each year.
movie(id, title, yr, score, votes, director)
casting(movieid, actorid, ord)
SELECT m.yr, COUNT(*) AS num_movies FROM MOVIE m JOIN CASTING c ON c.movieid = m.id JOIN ACTOR a ON a.id = c.actorid AND a.name = 'John Travolta' GROUP BY m.yr ORDER BY num_movies DESC, m.yr DESC
num_movies DESC will put the highest values at the top of the resultset. If numerous years have the same count, the
m.yr will place the most recent year at the top... until the next
num_movies value changes.
No, you can not layer aggregate functions on top of one another in the same SELECT clause. The inner aggregate would have to be performed in a subquery. IE:
SELECT MAX(y.num) FROM (SELECT COUNT(*) AS num FROM TABLE x) y