mysql - 删除时的 MySQL 错误

Question

我尝试从表中删除一行，但是当我尝试时出现错误：#1241 - Operand should contain 1 column(s)

我的查询是：DELETE FROM Posts WHERE idPosts = 6;

我不明白为什么我不能删除帖子（idPosts = 6 的帖子存在）

我的桌子上也有一个触发器：

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

在您的触发器中，您正在执行一项操作SELECT *，而您应该只选择与 lastPost 对应的列。我想这就像SELECT postId

Answer 2

UPDATE Topics SET lastPost = ( SELECT * FROM Posts WHERE idTopic = old.idTopic ORDER BY datePosts DESC LIMIT 1) WHERE idTopics = old.idTopic;

SELECT * 正在返回几列，请尝试 SELECT ID