我可以从 2 个不同表的主键为第三个表创建复合键吗？ MySQL支持吗？

Question

I have got 3 different tables:

review table-> this has mov_id as the primary key. users_table -> this has username as the primary key. review_table -> can I make a composite primary key for this table from movie_id and username?

users table

reviews table

comments table

I can't connect these 3 tables and I can't figure out why.

This is the error I'm getting while creating the comments table

Answer 1

You can create composite primary key with foreign keys (primary keys from others tables), you have nothing special to do. Just constrain the foreign keys and declare them as primary.

With the names of tables and columns you provided, here's a query to create the table you want:

CREATE TABLE review_table (
  movie_id INT,
  username VARCHAR(255),
  -- Change INT and VARCHAR(255) by what you used on the others tables
  PRIMARY KEY (movie_id, username),
  FOREIGN KEY (movie_id) REFERENCES movies_table(movie_id),
  FOREIGN KEY (username) REFERENCES users_table(username)
)