WTO对与GROUP BY表和ORDER BY MAX（）

Question

此代码正常工作

SELECT 
    c.id_article, 
    a.titre AS title_article 
FROM comments AS c 
LEFT JOIN articles AS a 
    ON a.id = c.id_article 
WHERE c.hide = 0 
GROUP BY c.id_article 
ORDER BY MAX(c.date) DESC 
LIMIT 0, 6 

但我需要在最后文章评论的用户名。

我试试这个

SELECT 
    c.id_article, 
    a.titre AS title_article, 
    u.nom_utilisateur AS user_name 
FROM comments AS c 
LEFT JOIN articles AS a 
    ON a.id = c.id_article 
LEFT JOIN membres AS u 
    ON c.id_user = u.id 
WHERE c.hide = 0 
GROUP BY c.id_article 
ORDER BY MAX(c.date) DESC 
LIMIT 0, 6 

和不工作...

任何帮助吗？

（对不起我的英文不好...）

Answer 1

没有错误消息或说明什么是错了，它是一种很难说，但在任何情况下，你没有包括在GROUP BY声明u.nom_utilisateur 。

MySQL通常允许这个没有抛出错误，但它可能会导致意想不到的结果。

SELECT 
    c.id_article, 
    a.titre AS title_article, 
    u.nom_utilisateur AS user_name 
FROM comments AS c 
LEFT JOIN articles AS a 
    ON a.id = c.id_article 
LEFT JOIN membres AS u 
    ON c.id_user = u.id 
WHERE c.hide = 0 
GROUP BY c.id_article, u.nom_utilisateur 
ORDER BY MAX(c.date) DESC 
LIMIT 0, 6 

Answer 2

我有一个部分的解决方案。

我使用此代码从文章检索最后意见：

SELECT 
    c.id_article, 
    MAX(c.id) AS last_id_comment, 
    a.titre AS title_article 
FROM comments AS c 
LEFT JOIN articles AS a 
    ON a.id = c.id_article 
WHERE c.hide = 0 
GROUP BY c.id_article 
ORDER BY MAX(c.date) DESC 
LIMIT 0, 6 

和之后而第一选择，我使用此代码为检索来自最后的评论用户名：

SELECT 
    u.nom_utilisateur AS username 
FROM comments AS c 
LEFT JOIN membres AS u 
    ON u.id = c.id_user 
WHERE c.id = :last_id_comment 

不是最好的解决方案，但它的工作。