mysql 中的运行平均值

我有如下表

id   timestamp  speed
1    11:00:01   100
2    11:05:01   110
3    11:10:01   90
4    11:15 :01  80

我需要计算移动平均线，如下所示

id   timestamp  speed average
1    11:00:01   100   100 
2    11:05:01   110   105
3    11:10:01   90    100
4    11:15:01   80    95

我尝试过的

SELECT 
*,
(select avg(speed) from tbl t where tbl.timestamp<=t.timestamp) as avg
FROM 
tbl

乍一看很简单，但是当表上的数据膨胀时，就太慢了

还有更快的方法吗？

您的查询是执行运行平均值的一种方法：

SELECT t.*,
       (select avg(speed) from tbl tt where tt.timestamp <= t.timestamp) as avg
FROM tbl t;

另一种方法是使用变量：

select t.*, (sum_speed / cnt) as running_avg_speed
from (select t.*, (@rn := @rn + 1) as cnt, (@s := @s + speed) as sum_speed
      from tbl t cross join
           (select @rn := 0, @s := 0) params
      order by timestamp
     ) t;

上的索引tbl(timestamp)应进一步提高性能。