Question

我有一张用户观看历史记录表。我记录了＆＃39; content_id＆＃39;，＆＃39; user_id＆＃39;并在名为＆＃39; watch_history＆＃39;的表格中添加时间戳。每次查看内容。即使连续多次观看相同的内容，也会记录每次点击。

我需要提取观看记录，但是＆＃39; content_id＆＃39;列应该是不同的，并按照最近观看的顺序排序...我发现很难解释，但基本上确切地说YouTube观看历史记录的工作原理（没有同一视频的多个实例）。

这是我到目前为止所做的：

SELECT content_id, time_stamp, user_id, 
     COUNT(DISTINCT content_id) AS hit_count 
FROM watch_history 
WHERE user_id = X 
GROUP BY content_id 
ORDER BY time_stamp DESC

它有效，但我需要＆＃39; time_stamp＆＃39;字段反映最后一次观看内容，有什么帮助吗？

感谢。

Answer 1

SELECT中的列不在GROUP BY中。这对于user_id来说是可以接受的，因为它是固定值。但对timestamp来说，这不行。

使用MAX()聚合功能：

SELECT content_id, MAX(time_stamp) as time_stamp, user_id, 
       COUNT(*) AS hit_count 
FROM watch_history 
WHERE user_id = X 
GROUP BY content_id, user_id
ORDER BY MAX(time_stamp) DESC;

注意：COUNT(DISTINCT content_id)没有意义。它将在每一行返回“1”（除非有content_id为NULL的行）。我想你只想要COUNT(*)。

Answer 2

您希望按最新内容视图排序匹配，还是按特定查看者对内容的最新视图进行排序？

如果答案是前者，那么：

SELECT content_id, user_id, 
     COUNT(content_id) AS hit_count 
FROM watch_history h
WHERE user_id = X 
GROUP BY content_id
ORDER BY (Select Max(timestamp) from watch_history 
          Where user_id = X 
             and content_id = h.content_id) DESC

或

SELECT content_id, time_stamp, user_id, 
     COUNT(content_id) AS hit_count 
FROM watch_history h
   join watch_history last
       on last.content_id = h.Content_id
          and last.timestamp = 
              (Select max(timestamp) FROM watch_history 
               where user_id = X 
                  and content_id = h.content_id)
WHERE user_id = X 
GROUP BY content_id, time_stamp
ORDER BY last.timestamp desc

MySQL分组排序问题

2 个答案: