您有一个每天分组的查询，例如：

select 
  the_date as day,
  sec_to_time(avg(timestampdiff(second, start_time, end_time))) as duration
from ...
group by the_date;

你希望1-7天，8-14天，15-21天，22天每月结束。使用 CASE WHEN 建立团队。

select 
  year(the_date) as year,
  month(the_date) as month,
  case 
    when day(the_date) <=  7 then '01-07'
    when day(the_date) <= 14 then '08-14'
    when day(the_date) <= 21 then '15-21'
    else                          '22-end'
  end as day_range,
  sec_to_time(avg(timestampdiff(second, start_time, end_time))) as duration
from ...
group by year, month, day_range
order by year, month, day_range;