检索每n行的最高值

[英]Retrieve highest value per n rows


I have a table where each row contains a value and a datetime. It has hundreds of thousands of rows. I would like to select the highest (max) value every n rows.

我有一个表,其中每行包含一个值和一个日期时间。它有数十万行。我想每n行选择最高(最大)值。

I had previously used a query to get the highest value every hour, but this isn't quite what I am looking for:

我之前使用过查询来获得每小时最高的值,但这不是我想要的:

SELECT datetime, MAX(value)
FROM `table` 
GROUP BY date_format(datetime, '%Y-%m-%d &h')

Any advice would be greatly appreciated!

任何建议将不胜感激!

1 个解决方案

#1


1  

You can enumerate the rows and then aggregate to your heart's desire:

您可以枚举行然后聚合到您心中的愿望:

select min(rn), max(rn), min(datetime), max(datetime), max(value)
from (select t.*, (@rn := @rn + 1) rn
      from `table` t cross join
           (select @rn := 0) params
      order by datetime
     ) t
group by floor((rn - 1) / @n)
order by min(rn);

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