如果您运行的是mysql 8.0，则可以使用窗口函数：

select request, created_at, expiry_date
from (
    select 
        t.*,
        lag(expiry_date) over(order by request) lag_expiry_date
    from mytable t
) t
where lag_expiry_date is date or created_at > lag_expiry_date

另一方面，如果您想根据与上一个有效记录的差异以增量方式选择记录，那么就要复杂一些。您需要某种迭代过程，它建议使用递归查询。基本上，您可以用 row_number() ，然后逐一处理，决定保留哪一个。

with recursive 
    data as (
        select t.*, row_number() over(order by created_date) rn from mytable t
    ),
    cte as (
        select d.*, 1 to_keep, expiry_date last_expiry_date 
        from data d 
        where rn = 1 
        union all
        select 
            d.*,
            (d.created_date > c.last_expiry_date),
            case when d.created_date > c.last_expiry_date 
                then d.expiry_date 
                else c.last_expiry_date
            end
        from cte c
        inner join data d on d.rn = c.rn + 1
    )
select request_id, created_date, expiry_date 
from cte 
where to_keep
order by rn

db小提琴演示：

| request_id | created_date | expiry_date |
| ---------- | ------------ | ----------- |
| 1          | 2020-06-02   | 2020-06-06  |
| 3          | 2020-06-08   | 2020-06-12  |
| 6          | 2020-06-18   | 2020-06-20  |
| 7          | 2020-06-21   | 2020-06-25  |