SQL - Get highest rated movie by genre - sql

Question

I have three tables:
CREATE TABLE Movie
(
movieId INTEGER GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
title VARCHAR(255) NOT NULL,
moviePath VARCHAR(500) NOT NULL
);
CREATE TABLE Rating
(
rid INTEGER GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
mid INTEGER FOREIGN KEY REFERENCES Movie(movieId) ON DELETE CASCADE,
uid INTEGER FOREIGN KEY REFERENCES User(id) ON DELETE CASCADE,
rating INTEGER NOT NULL,
);
CREATE TABLE Genre(
id INTEGER GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
movieId INTEGER NOT NULL FOREIGN KEY REFERENCES Movie(movieId) ON DELETE CASCADE,
genre VARCHAR(255) NOT NULL
);
I want to create an sql query which gives me the most seen movie(with moviepath, title) from the the most seen genre back.
Any ideas?
UPDATE
Results:
| MID | TITLE | MOVIEPATH |
--------------------------------
| 4 | Happy days | a |
| 4 | Happy days | a |

Answer 1

It's really great if you had provided some sample data to match.. Well try this out. Looking at your earlier question this answer is drafted.
SQLFIDDLE DEMO
select t.mid, t.sum_rating,
m.title, m.moviepath, g.genres
from (
select mid,
sum(rating) as sum_rating,
dense_rank() over (order by
sum(rating) desc) as rnk
from rating
group by mid
) t
left join movie m
on m.movieid = t.mid
left join genre g
on g.movieid = m.movieid
where t.rnk = 1;
Results:
| MID | SUM_RATING | TITLE | MOVIEPATH | GENRES |
------------------------------------------------------
| 4 | 37 | Happy days | a | comedy |
| 4 | 37 | Happy days | a | RomCom |
You may use this alternative as HSQL doesn't support dense_rank:
SQLFIDDLE DEMO ALTERNATIVE
Query with : order by desc and top 1
-- alternatively
select t.mid, t.sum_rating,
m.title, m.moviepath, g.genres
from (
select top 1 mid,
sum(rating) as sum_rating
from rating
group by mid
order by sum_rating desc
) t
left join movie m
on m.movieid = t.mid
left join genre g
on g.movieid = m.movieid
;

Answer 2

You could calculate the rating by summing all ratings for a movie in a subquery. Another subquery could calculate the highest rating per genre. By joining them together, you'd filter only the top movies per genre:
select *
from Movie m
join Genre g
on g.movieId = m.movieId
join (
select r.mid
, sum(Rating) as SumRating
from Rating r
group by
r.mid
) r
on r.mid = m.movieId
join (
select g.id as gid
, max(SumRating) as MaxGenreRating
from (
select r.mid
, sum(Rating) as SumRating
from Rating r
group by
r.mid
) r
join Genre g
on g.movieId = r.mid
group by
g.id
) filter
on filter.gid = g.id
and filter.MaxGenreRating = r.SumRating

Answer 3

Where can we found the count of views? With this tables you can find the highest rated movie by using a query like this:
select Movie.movieId, Movie.title, Movie.moviepath
from movie, rating, genre
where
movie.id = rating.mid and
movie.id = genre.movieId
order by rating desc
limit 1; // limit is used if you are using MySQL. In other databases you can use suitable sql query.
But if you are looking for the most seen movie from most seen genre, you have to have the view count of each movie and each genre inside your tables.

Answer 4

I can recommend you using aggregate max on the rating together with group by on genre
select max(Rating.rating) as max_rating, Genre.genre, Movie.movieId from Movie
inner join Rating on Movie.movieId = Rating.mid
inner join Genre on Movie.movieId = Genre.movieId
group by Genre.genre;
I am not so sure that this will work 100% since I didn't try it, but I the idea is to use group by. It it ment to be used with aggregates like count, max, min, avg and so on.
I hope that helps