Question

我编写了下一个查询SQL，用于通过重新注释获取最后的注释：

SELECT c.*, ar.ArticleName, ar.idArticle, du.DetailToUsersName, du.DetailToUsersPhoto, COUNT(c.idCommentToArticle) AS CNT, CASE WHEN d.Count IS NULL THEN 0 ELSE d.Count END AS CountLikes 
FROM commenttoarticle c 

INNER JOIN (SELECT CommentToArticlePID FROM commenttoarticle 
GROUP BY CommentToArticlePID 
ORDER BY CommentToArticlePID LIMIT 3) AS articleComments 
USING (CommentToArticlePID) 

LEFT JOIN article ar ON c.CommentToArticleIdArticle = ar.idArticle 
LEFT JOIN detailtousers du ON du.idDetailToUsers = c.CommentToArticleIdUser 
LEFT JOIN `likes` d ON (d.IdNote = c.idCommentToArticle AND d.LikeType = 6) 

WHERE c.CommentToArticleIdArticle = 11 
GROUP BY c.idCommentToArticle

那么，为什么子查询选择中的运算符LIMIT 3不起作用？现在，此查询显示表commenttoarticle

中的所有行

我似乎需要像以下那样做一些思考：

SELECT...
FROM (select * from commenttoarticle commenttoarticle c INNER JOIN
            (SELECT distinct(CommentToArticlePID)
              FROM commenttoarticle b
                ORDER BY CommentToArticlePID
                   LIMIT  2) AS commenttoarticle USING (CommentToArticlePID)) as c

          LEFT JOIN article ar ON c.CommentToArticleIdArticle = ar.idArticle...

转储表评论文章：

CREATE TABLE IF NOT EXISTS `commenttoarticle` (
  `idCommentToArticle` int(11) NOT NULL AUTO_INCREMENT,
  `CommentToArticleTime` int(11) NOT NULL,
  `CommentToArticleIdArticle` int(11) NOT NULL,
  `CommentToArticleComment` text NOT NULL,
  `CommentToArticleIdUser` int(11) NOT NULL,
  `CommentToArticlePID` int(11) NOT NULL,
  PRIMARY KEY (`idCommentToArticle`),
  UNIQUE KEY `idCommentToArticle_UNIQUE` (`idCommentToArticle`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=59 ;


INSERT INTO `commenttoarticle` (`idCommentToArticle`, `CommentToArticleTime`, `CommentToArticleIdArticle`, `CommentToArticleComment`, `CommentToArticleIdUser`, `CommentToArticlePID`) VALUES
(29, 0, 11, 'продажам?\nИнтересует не мега-звезда, а именно предметный, руками умеющий продавать сам и помогающий выстраивать это бизнесам.', 459, 0),
(30, 0, 11, '2', 459, 0),
(31, 0, 11, '3', 459, 0),
(36, 0, 11, '3.1', 459, 31),
(37, 1413822798, 11, 'also facing that prob. on the plteform of win 7', 459, 29),
(38, 0, 11, ' here i dont have internet connection.. @Samint Sinha thanks ill check it out maybe tomorrow.', 459, 29),
(39, 0, 11, ' Select max id and you will have dhe last row returned', 459, 29),
(32, 0, 11, '4', 459, 0),
(44, 1414354324, 11, 'How to do', 456, 29),
(45, 1414354469, 11, 'sfsfsf', 456, 29),
(46, 1414354708, 11, 'dddd', 456, 29),
(47, 1414357761, 11, 'sfsfs', 456, 0),
(57, 1414370833, 39, 'kkkppppppp', 456, 0),
(49, 1414358233, 11, 'VSF\nSFSF', 456, 0),
(50, 1414359589, 11, 'How to do', 456, 0),
(51, 1414359660, 11, 'sfsfsdf', 456, 0),
(52, 1414361057, 11, 'SDFSF', 456, 0),
(53, 1414364023, 11, 'dsfdsjfsifmsi', 456, 0),
(54, 1414364031, 11, 'sdfdskjfnskf', 456, 52),
(55, 1414364034, 11, 'sdfdskjfnskf', 456, 52),
(56, 1414364044, 11, 'fndsdfnsofosfi', 456, 52),
(58, 1414370841, 39, 'dfgdfgdgdgdgdgdfgdgdfg', 456, 0);

转储表文章：

CREATE TABLE IF NOT EXISTS `article` (
  `idArticle` int(11) NOT NULL AUTO_INCREMENT,
  `ArticleName` varchar(255) NOT NULL,
  `ArticleTime` int(11) NOT NULL,
  `ArticleDescription` varchar(500) NOT NULL,
  `ArticleText` text NOT NULL,
  `ArticleToUserID` int(11) DEFAULT NULL,
  `ArticleCategory` int(11) NOT NULL,
  `ArticleView` int(11) NOT NULL,
  `ArticleCountry` int(11) NOT NULL,
  `ArticlePhoto` varchar(150) NOT NULL,
  `ArticleCity` int(11) NOT NULL,
  PRIMARY KEY (`idArticle`),
  UNIQUE KEY `idArticle_UNIQUE` (`idArticle`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=50 ;

Answer 1

The USING(column_list) clause names a list of columns that must exist in both tables.

参考：http://dev.mysql.com/doc/refman/5.0/en/join.html

CommentToArticlePID不在您的第一张桌子中。

另外，加入单列有什么意义？是的，如果你想限制，这可能适用，但为什么我们LIMIT？

Answer 2

通过在评论上构建自联接，你不是限制，而是将结果相乘。您需要的是评论表上的单个子查询

SELECT c.*, ar.ArticleName,
    ar.idArticle, du.DetailToUsersName,
    du.DetailToUsersPhoto, COALECSE(SUM(d.count), 0)
FROM 
    (SELECT *
     FROM 
         commenttoarticle
     WHERE
         CommentToArticleIdArticle = 11
     ORDER BY
         CommentToArticlePID, idCommentToArticle DESC
     LIMIT 3
    ) c
LEFT JOIN 
    article ar
    ON c.CommentToArticleIdArticle = ar.idArticle 
LEFT JOIN
    detailtousers du
    ON du.idDetailToUsers = c.CommentToArticleIdUser 
LEFT JOIN
    likes d
    ON (d.IdNote = c.idCommentToArticle AND d.LikeType = 6)
GROUP BY
    c.idCommentToArticle

我假设注释可以在likes表中有多个条目，否则子查询和group by不是必需的。

为什么操作员LIMIT无法正常工作？

2 个答案: