SQL: create a view comparing different rows - sql

Question

I have data for movies that looks something like this:
cast_id | cast_name | movie_id
1 A 11
2 B 11
3 C 11
4 D 12
5 E 12
1 A 13
I want to create a view where I compare two different cast members so that I will start with something like this:
CREATE VIEW compare(cast_id_1, cast_id_2, num_movies);
SELECT * FROM compare LIMIT 1;
(1,2,2)
where I am looking at actor A and actor B, who have a total of 2 movies between the two of them.
Not sure how to compare the two different rows and my searchers so far have been unsuccessful. Any help is much appreciated!

Answer 1

That's a self-join:
create view myview as
select t1.cast_id cast_id_1, t2.cast_id cast_id_2, count(*) num_movies
from mytable t1
inner join mytable t2 on t2.movie_id = t1.movie_id and t1.cast_id < t2.cast_id
group by t1.cast_id, t2.cast_id
Thives generates all combinations of cast members that once appeared in the same movie, with the total number of movies. Join condition t1.cast_id < t2.cast_id is there to avoid "mirror" records.
You can then query the view. If you want members that have two common movies (which is actually not showing in your sample data...):
select * from myview where num_movies = 2

Answer 2

I'm thinking a procedure might be helpful. This stored procedure takes the 2 cast_id's and num_movies as input parameters. It selects the movie_id's of the movies the two cast_id's have appeared in together. Then based on whether or not that number exceeds the num_movies parameter: either 1) a list of movies (release dates, director, etc.) is returned, else the message 'Were not in 2 movies together' is returned.
drop proc if exists TwoMovieActors;
go
create proc TwoMovieActors
#cast_id_1 int,
#cast_id_2 int,
#num_movies int
as
set nocount on;
declare #m table(movie_id int unique not null,
rn int not null);
declare #rows int;
with
cast_cte as (
select *, row_number() over (partition by movie_id order by cast_name) rn
from movie_casts mc
where cast_id in(#cast_id_1, #cast_id_2))
insert #m
select movie_id, row_number() over (order by movie_id) rn
from cast_cte
where rn=2
select #rows=##rowcount;
if #rows<#num_movies
select concat('Were not in ', cast(#num_movies as varchar(11)), ' movies together');
else
select m.movie_id, mv.movie_name, mv.release_date, mv.director
from #m m
join movies mv on m.movie_id=mv.movie_id;
To execute it would be something like
exec TwoMovieActors 1, 2, 2;