mysql查询以获取不同phone_numbers的最新N行的平均值

Question

我的表是 (phone_number, bpm, timestamp)。我想获取每个 phone_number 的最新 10 行的 phone_number, avg(bpm)。我试过了。。

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

此查询给出空结果。我不能在我的 mysql 版本中使用 IN 子句。

Answer 1

这对 MySQL 来说是个痛点。最合理的解决方案是使用变量来枚举行然后聚合：

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;