SQL：选择包含评论数量和最新评论日期的项目

Question

我想显示包含评论数量和最后评论日期的项目，每个项目。

SELECT item.*, 
    count(comments.itemid) AS commentcount, 
    comments.created AS commentcreated 
FROM table_items AS item 
LEFT JOIN table_comments AS comments ON (comments.itemid = item.id) 
WHERE item.published=1 
GROUP BY item.id 
ORDER BY item.created DESC 

现在commentcreated值是第一个评论的日期：我想要最后一条评论。排序依据在LEFT JOIN上不起作用。这如何实现？

Answer 1

尝试

SELECT item.*, 
    count(comments.itemid) AS commentcount, 
    max(comments.created) AS commentcreated 
FROM table_items AS item 
LEFT JOIN table_comments AS comments ON (comments.itemid = item.id) 
WHERE item.published=1 
GROUP BY item.id 
ORDER BY item.created DESC 

你需要告诉MySQL与MAX（），MIN（）或其他聚合函数使用哪一个组中的日期。