Schemas:
CREATE TABLE todo_users ( user_id SERIAL PRIMARY KEY, name VARCHAR(50) NOT NULL, email VARCHAR(50) UNIQUE NOT NULL, password VARCHAR(100) NOT NULL, sex VARCHAR(50) NOT NULL, color VARCHAR(50) NOT NULL, age VARCHAR(50) NOT NULL );
CREATE TABLE todo_tasks ( task_id SERIAL PRIMARY KEY, task VARCHAR(255) NOT NULL, user_id INT REFERENCES todo_users(user_id) ON DELETE CASCADE );
CREATE TABLE todo_user_task_link ( user_task_link_id SERIAL PRIMARY KEY, task_id_link INT REFERENCES todo_tasks(task_id) ON DELETE CASCADE, user_id_link INT REFERENCES todo_users(user_id) ON DELETE CASCADE );
CREATE TABLE todo_friends ( friends_id SERIAL PRIMARY KEY, user_id INT REFERENCES todo_users(user_id) ON DELETE CASCADE, added_friend_id INT REFERENCES todo_users(user_id) ON DELETE CASCADE );