限制查询结果

Question

我有一个应用程序，其中包含音乐排行榜，以展示热门曲目（显示前十名）。

但是，我试图限制图表，以便任何特定用户不能同时在顶部图表上拥有多个轨道。

如果您需要更多信息，请告诉我。

Answer 1

您可以使用row_number()函数提供一个运行编号，该编号在用户ID更改时会重置。 然后可以在WHERE子句中使用它来创建每个用户限制：

SELECT * FROM (
    SELECT COALESCE(sum(plays.clicks), 0),
        row_number() OVER (PARTITION BY users.id ORDER BY COALESCE(sum(plays.clicks), 0) DESC),
        users.id AS user_id,
        tracks.*
        FROM tracks
            JOIN plays
            ON tracks.id = plays.track_id
            AND plays.created_at > now() - interval '14 days'
            INNER JOIN albums
            ON tracks.album_id = albums.id
            INNER JOIN users
            ON albums.user_id = users.id
            GROUP BY users.id, tracks.id
            ORDER BY 1 desc) sq1
    WHERE row_number <= 2 LIMIT 10;