need help creating a simple many-to-many relationship using mysql - mysql

Question

So I got used to using doctrine so much that I forgot the standard mysql syntax, which I need for an exam.
I want to create a test database called 'youtube'
with an app_users table and an app_videos table.
In "real life" this would be a oneToMany relationship, but I need to
study to create a manyToMany relationship.
so its
"many app_users" -> have "many app_videos"
and the other way around.
so first I created a database;
CREATE DATABASE youtube;
use youtube;
then I created the users and videos table
CREATE TABLE app_users(
id INT AUTO_INCREMENT,
username VARCHAR(20),
password VARCHAR(40),
first_name VARCHAR(20),
last_name VARCHAR(20),
video_id INT,
PRIMARY KEY(id)
);
CREATE TABLE app_videos(
id INT AUTO_INCREMENT,
video_path VARCHAR(20),
description VARCHAR(20),
likes INT(20),
dislikes INT(20),
user_id INT,
PRIMARY KEY(id)
);
then I created a relationship table
CREATE TABLE vid_uid
(
id INT AUTO_INCREMENT,
video_id INT,
user_id INT,
PRIMARY KEY(id)
);
now what I need to do is somehow connect the columns to eachother but my syntax never works
I know I need to change this
ALTER TABLE app_users
ADD FOREIGN KEY(video_id)
REFERENCES app_videos(video_id);
to something that works :/

Answer 1

You need to change app_videos(video_id) to app_videos(id). Also you want to alter the table vid_uid (not app_users) since thats the one that as references to external keys:
ALTER TABLE vid_uid
ADD FOREIGN KEY(video_id)
REFERENCES app_videos(id);
You'll also need to do:
ALTER TABLE vid_uid
ADD FOREIGN KEY(user_id)
REFERENCES app_users(id);