Nesting SELECT statements with duplicate entries and COUNT - sql

Question

I'm working with 3 tables: actors, films, and actor_film. Actors and films only have 2 fields: id (primary key) and name. Actor_film also has 2 fields, actor and film, which are both foreign keys representing actor and film ids, respectively. So if a film had 4 actors in it, there'd be 4 actor_film entries with the same film and 4 different actors.
My problem is that, given a certain actor's id, I'd like to return the actor id, actor name, film name, and the total number of actors in that film. However, the only actors that I want to show are ones that contain certain letters in their names.
Let me clear things up with an example. Say Tom Hanks is in only 2 movies, Forrest Gump and Saving Private Ryan, and I'm looking for actors in those 2 movies that have "Gary" or "Matt" in their names. Further suppose that there are 4 actors in Forrest Gump, and 5 in Saving Private Ryan. Then, the only thing I'd want to return would be (without the column names, of course)
actor id | actor name | film name | # actors
abcdefg | Gary Sinise | Forrest Gump | 4
hijklmn | Matt Damon | Saving Private Ryan | 5
opqrstu | Paul Giamatti | Saving Private Ryan | 5
Currently, I'm 75% of the way there by using:
SELECT actor.id, actors.name, films.name,
FROM (
SELECT actor_film.film
FROM actor_film, actors
WHERE actor_film.actor = actors.id
) AS a, actor_film, actors, films
WHERE actor_film.film = a.film
AND actors.id = actor_film.actor
AND films.id = a.film;
This is returning stuff like:
arnie | Arnold Schwarzenegger | Around the World in 80 Days
arnie | Arnold Schwarzenegger | Around the World in 80 Days
for a film that has 2 actors in it. In other words, I can't pull out all the distinct actors in the movie, but get the proper count for it implicitly and not explicitly with COUNT.
Anyway, I think I'm looking for some kind of INNER JOIN or nested SELECT, but I'm new to SQLite3 and don't know how to bring these together. Any solutions would be great, and any explanations on top of that would be amazing as well.

Answer 1

You shouldn't use the old style joins. They were old in '95 when the newer standard that let you do left joins clearer was made a standard.
I've noticed you also use plurals for your table names (eg "actors") The standard style is to use the singular for the table table name (eg "actor")
I use both these suggestions below, I also show you each step. I suggest you run the queries for each step and look at the output to understand how everything works since you are new to SQL.
Ok, lets take you problem step by step. First of all to see each actor and the films they are in (your first 3 columns) do this:
SELECT a.id as actor_id, a.name as actor_name, f.name as film_name
FROM actor as a
JOIN actor_film af on a.id = af.actor
JOIN film as f on af.film = f.id
Your last column can be found with the following query:
SELECT af.film as film_id, count(*) as c
FROM actor_film as af
GROUP BY af.film
Now we just join them together
SELECT a.id as actor_id, a.name as actor_name, f.name as film_name, fc.c as num_actors
FROM actor as a
JOIN actor_film af on a.id = af.actor
JOIN film as f on af.film = f.id
JOIN (
SELECT af.film as film_id, count(*) as c
FROM actor_file as af
GROUP BY af.film
) as fc on af.film = fc.film_id
If you want you can add a
WHERE a.name = 'Gary' OR a.name = 'Matt'
depending on your platform you might want
WHERE lower(a.name) = 'gary' OR lower(a.name) = 'matt'