Can't write to MySQL database?

Question

MySQL

I have a table that has the following columns: receiver_id , author_id , article_id and liked. There is no id column.
The following unique index is worth: receiver_id, author_id, article_id, liked.

When I make a request like this:

INSERT INTO likes (receiver_id, author_id, article_id, liked) VALUES (412, 13, 23, 1)

then the request passes. But when I do the same, only change the article_id, the request fails:

INSERT INTO likes (receiver_id, author_id, article_id, liked) VALUES (412, 13, 24, 1)

Why? When changing the article_id, the index is unique in any case

Answer 1

Found an error. Didn't notice that `receiver_id` is PRIMARY KEY, so error 1062 is thrown.