Question

CREATE TABLE `comments` (
  `comment_id` int(11) NOT NULL AUTO_INCREMENT,
  `comment_parent_id` int(11) NOT NULL DEFAULT '0',
  `user_id` int(11) NOT NULL DEFAULT '0',
  `comment_text` varchar(200) NOT NULL DEFAULT '',
  `comment_created` int(20) NOT NULL DEFAULT '0',
  `comment_updated` int(20) NOT NULL DEFAULT '0',
  `comment_replies_count` int(11) NOT NULL DEFAULT '0',
  PRIMARY KEY (`comment_id`)
) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=latin1

每个评论都可以有多个回复，但是无法回复回复。因此，当有人回复评论时，他们插入的行将具有他们在父ID列中回复的评论的ID。

我想检索所有评论，如果评论有回复，我想检索最后的回复。

SELECT c1.* 
FROM comments c1 
WHERE comment_parent_id = '0' 
ORDER BY comment_created DESC;

So if c1.comment_replies_count > 0 I would like to... 

SELECT c2.* 
FROM comments c2 
WHERE comment_parent_id = c1.comment_id 
ORDER BY comment_created DESC Limit 1;

这可以在1个查询中实现吗？或者，最好在php循环语句中再次调用数据库，以获取对注释的最后一个回复？

提前致谢，请原谅我的无知，因为我还在学习。

Answer 1

您可以将表格重新加入自身：

SELECT c1.*, c2.*, MAX(c2.comment_id)
FROM comments c1 LEFT JOIN comments c2 ON c1.comment_id = c2.comment_parent_id
WHERE c1.comment_parent_id = '0' 
GROUP BY c1.comment_id
ORDER BY c1.comment_created DESC

Answer 2

尝试子选择：

SELECT * FROM comments WHERE comment_parent_id in (
SELECT c1.comment_id 
FROM comments c1 
WHERE c1.comment_parent_id = '0' 
AND c1.comment_replies_count > 0
ORDER BY comment_created DESC)
ORDER BY comment_created DESC Limit 1;

MySQL SELECT带有条件帮助

2 个答案: