SQL - List attributes that showed up with others - mysql

Question

I am working on an assignment that requires me to list the actors and actresses that show up in a movie, and then the actors and actresses that have starred with them in other movies. A diagram of the database is viewable here: http://i.imgur.com/kj8qVgF.png
I have a query for the first part (getting the names of actors and actresses that show up in a certain movie).
SELECT DISTINCT n.name
FROM cast_info c
INNER JOIN name n
ON (n.id = c.person_id)
INNER JOIN title t
ON (c.movie_id = t.id)
CROSS JOIN role_type r
WHERE (t.title = 'The Movie') AND (r.role = 'actress' OR r.role = 'actor')
Could I get some assistance to help me find the actresses and actors that star with them in other movies?
Example:
Actors in a given movie 'The Movie': Bob, Joe, Billy
Actors in a different movie 'Another Movie': Joe, Daniel, Frank
Actors in another different movie 'Third Movie': Billy, Susan, Theodore
It should return Daniel, Frank, Susan, and Theodore, because they starred in at least one movie with one of the actors in the given movie.

Answer 1

According to your example, and your model is 3NF, so you can use trivial IN to solve the problem just like you described in Natural language.
SELECT DISTINCT n.name
FROM cast_info c
INNER JOIN name n
ON (n.id = c.person_id)
INNER JOIN title t
ON (c.movie_id = t.id)
INNER JOIN role_type r
ON (c.role_id = r.id)
WHERE (r.role = 'actress' OR r.role = 'actor') -- find the actresses and actors ...
AND c.movie_id IN -- starred in at least one movie ...
(SELECT movie_id
FROM cast_info
WHERE id in -- with one of the actors in the given movie => Bob, Joe, Billy
(SELECT cc.id
FROM cast_info cc
INNER JOIN role_type rr
ON (cc.role_id = rr.id)
WHERE ( rr.role = 'actor') -- only select actors in the given movie
AND cc.movie_id in (select id from title where title = 'The Movie')
)
)
AND c.id NOT IN -- except the actors in the given movie
(SELECT cc.id
FROM cast_info cc
INNER JOIN role_type rr
ON (cc.role_id = rr.id)
WHERE ( rr.role = 'actor') -- only select actors in the given movie
AND cc.movie_id in (select id from title where title = 'The Movie')
)
This easy to translate Natural language to SQL but not efficient using IN, you can transfer IN with EXISTS, that would be more efficient.

Answer 2

So we meet again. Hopefully I can be of the same assistance as your last question. I like that you began by breaking this down into smaller parts. I would have started at the same place as you - getting all of the actors in the necessary movie. I've changed your query slightly, by selecting the persons id instead of their name so I can keep this answer a little shorter and cleaner.
SELECT c.person_id
FROM cast_info c
JOIN title t ON c.movie_id = t.id
JOIN role_type r ON c.role_id = r.id
WHERE t.title = 'The Movie' AND (r.role = 'actress' OR r.role = 'actor');
*Note, I did not use distinct here because a person should not appear in this movie as an actor or actress more than once, but c.person_id is not a unique key so it would not hurt to be sure.
Then we can get all of the movies with those actors in them. We can filter to avoid the original table.
SELECT t.id
FROM title t
JOIN cast_info c ON c.movie_id = t.id
WHERE t.title != 'The Movie'
AND c.person_id IN(SELECT c.person_id
FROM cast_info c
JOIN title t ON c.movie_id = t.id
JOIN role_type r ON r.id = c.role_id
WHERE t.title = 'The Movie' AND (r.role = 'actress' OR r.role = 'actor'))
Now we can pull all of the actors from all of those movies, and exclude our original actors. Here is where it is a good idea to use distinct person id. This is because Bob may star in 'The Movie'. Later, Bob did a movie with John, and another movie with John, but we don't want John to appear twice.
So, here is the final query:
SELECT DISTINCT c.person_id
FROM cast_info c
WHERE c.movie_id IN(SELECT t.id
FROM title t
JOIN cast_info c ON c.movie_id = t.id
WHERE t.title != 'The Movie'
AND c.person_id IN(SELECT c.person_id
FROM cast_info c
JOIN title t ON c.movie_id = t.id
JOIN role_type r ON r.id = c.role_id
WHERE t.title = 'The Movie' AND (r.role = 'actress' OR r.role = 'actor')))
AND c.person_id NOT IN(SELECT c.person_id
FROM cast_info c
JOIN title t ON c.movie_id = t.id
JOIN role_type r ON r.id = c.role_id
WHERE t.title = 'The Movie' AND (r.role = 'actress' OR r.role = 'actor'))
As I've said before, it's difficult to test this without data, and it's a lot of tables to make a simple SQL Fiddle, so please try these in bits like I have written them if they don't work, and let me know what may need to be tweaked.