SQL：選擇包含評論數量和最新評論日期的項目

Question

我想顯示包含評論數量和最後評論日期的項目，每個項目。

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 

現在commentcreated值是第一個評論的日期：我想要最後一條評論。排序依據在LEFT JOIN上不起作用。這如何實現？

Answer 1

嘗試

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 

你需要告訴MySQL與MAX（），MIN（）或其他聚合函數使用哪一個組中的日期。