mysql查詢從不同的phone_numbers獲得最新N行的平均值

Question

我的表是（phone_number，bpm，timestamp）。我想獲取每個phone_number的最新10行的phone_number，avg（bpm）。我試過了..

SELECT phone_number, AVG(bpm) 
FROM (
SELECT * 
FROM table_name 
WHERE bpm !=0 
ORDER BY timestamp DESC 
) AS temp 
GROUP BY phone_number 
HAVING COUNT(*) <=10 

此查詢給出空的結果。我不能在我的mysql版本中使用IN子句。

Answer 1

這是MySQL的一種痛苦。最合理的解決方案使用變量枚舉行，然後聚合：

SELECT phone_number, AVG(bpm) 
FROM (SELECT t.*, 
      (@rn := if(@pn = phone_number, @rn + 1, 
         if(@pn := phone_number, 1, 1) 
         ) 
      ) as rn 
     FROM table_name t CROSS JOIN 
      (SELECT @pn := '', @rn := 0) params 
     WHERE bpm <> 0 
     ORDER BY phone_number, timestamp DESC 
    ) t 
WHERE rn <= 10 
GROUP BY phone_number;