限制查詢結果

Question

我有一個包含音樂排行榜的應用程序來展示頂級曲目（它顯示前10名）。

但是，我試圖限制圖表，以便任何特定的用戶不能同時在頂部圖表上有多個軌道。

如果您需要更多信息，請讓我知道。

Answer 1

您可以使用row_number()函數，該函數提供一個在用戶標識更改時重置的運行編號。然後你可以使用在WHERE子句創建每個用戶的限制：

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;