--                 Exercises

--Q1 Find the titles of all movies directed by Steven Spielberg.
select title from Movie where director = "Steven Spielberg";

--Q2 Find all years that have a movie that received a rating of 4 or 5, and sort them in increasing order.
select distinct year from Movie, Rating
where Movie.mID = Rating.mID and
stars > 3 order by year;

--Q3 Find the titles of all movies that have no ratings.
select distinct title from Movie, Rating
where Movie.mID not in (select mID from Rating);

--Q4 Find the names of all reviewers who have ratings with a NULL value for the date.
select distinct name from Reviewer, Rating
where Reviewer.rID = Rating.rID and
Rating.ratingDate is NULL;

--Q5 Write a query to return the ratings data in a more readable format: reviewer name, movie title, stars, and ratingDate. Also, sort the data, first by reviewer name, then by movie title, and lastly by number of stars.
select distinct name as 'reviewer name', title as 'movie title', stars, ratingDate from
Movie, Rating, Reviewer
where
Movie.mID = Rating.mID and Rating.rID = Reviewer.rID
order by name, title, stars;

--Q6 For all cases where the same reviewer rated the same movie twice and gave it a higher rating the second time, return the reviewer's name and the title of the movie.
select name, title from Reviewer, Movie, Rating, Rating r2
where Rating.mID=Movie.mID and Reviewer.rID=Rating.rID
  and Rating.rID = r2.rID and r2.mID = Movie.mID
  and Rating.stars < r2.stars and Rating.ratingDate < r2.ratingDate;

--Q7 For each movie that has at least one rating, find the highest number of stars that movie received. Return the movie title and number of stars. Sort by movie title.
select title, max(stars) from Movie, Rating
where Movie.mID = Rating.mID
group by Rating.mID
order by title;

--Q8 For each movie, return the title and the 'rating spread', that is, the difference between highest and lowest ratings given to that movie. Sort by rating spread from highest to lowest, then by movie title.
select title, max(stars) - min(stars) as ratingSpread from Movie, Rating
where Movie.mID = Rating.mID
group by title
order by ratingspread desc, title;

--Q9 Find the difference between the average rating of movies released before 1980 and the average rating of movies released after 1980.
select smaller1980.second - bigger1980.first
from (select avg( averages1) as first
  from (select title, avg(stars) as averages1 from Movie, Rating where Movie.mID=Rating.mID and year > 1980 group by title)) as bigger1980,
(select avg( averages2) as second from (select title, avg(stars) as averages2 from Movie, Rating
      where Movie.mID=Rating.mID and year < 1980 group by title)) as smaller1980;