Question

I try to delete a row from my table, but when I try I get an error : #1241 - Operand should contain 1 column(s)

My query is : DELETE FROM Posts WHERE idPosts = 6;

I don’t understand why I can’t delete the post (the post with idPosts = 6 exists)

I have a trigger on the table too :

CREATE TRIGGER post_delete_update_lastPost_topic after delete on Posts for each row
BEGIN
  UPDATE Topics SET lastPost = (SELECT *
                                FROM Posts
                                WHERE idTopic = old.idTopic
                                ORDER BY datePosts DESC
                                LIMIT 1)
  WHERE idTopics = old.idTopic;
END $$

Answer 1

In your trigger you are doing a SELECT * whereas you should just select the column corresponding to lastPost. I suppose this is something like SELECT postId