Database design: foreign keys and normalization

Question

I'm new to database design so please bear with me. I'm using PHP and MySQL. I have a 'movies' table that contains some details about a movie. This includes genres, which have an (if I understand correctly) many to many relationship with movies, implying a single movie can belong to different genres and a single genre can belong to different movies.

From what I gather about database design, storing this kind of relationship in one table is not a good idea as it will either violate First Normal form or Second Normal form rules. How would I design my tables to avoid this; would I have to create a table for each genre separately or... ?

This leads my to my next question: separate tables need to have foreign keys to identify which information belongs to what row. In theory, if I had a unique key identifying each movie which I would then like to use to identify a director in a separate table, how would I create this relationship in MySQL?

Thank you for your time - if I've made anything unclear please let me know and I will try my best to clarify.

Answer 1

This includes genres, which have an (if I understand correctly) many to many relationship with movies, implying a single movie can belong to different genres and a single genre can belong to different movies.

That's right.

From what I gather about database design, storing this kind of relationship in one table is not a good idea

Right. You're looking for something loosely along these lines.

create table movies (
  movie_id integer primary key
  -- other columns
);

create table genres (
  genre varchar(15) primary key
  -- other columns?
);

create table movie_genres (
  movie_id integer not null,
  genre varchar(15) not null,
  primary key (movie_id, genre),
  foreign key (movie_id) references movies (movie_id),
  foreign key (genre) references genres (genre)
);

For directors, assuming there is only one director per movie, you can use this instead of the movies table above

create table movies (
  movie_id integer primary key,
  director_id integer not null,
  foreign key (director_id) references directors (director_id) -- not shown.
  -- other columns
);