DELETE FROM my_table
WHERE time <= (SELECT MAX(timeSet.time) FROM
(select time from (SELECT time FROM my_table ORDER BY time) where rownum<=N)
AS timeSet)
WHERE time <= (SELECT MAX(timeSet.time) FROM
(select time from (SELECT time FROM my_table ORDER BY time) where rownum<=N)
AS timeSet)
where time <= (select max(a.time) from
(select time from my_table order by time asc )a where ROWNUM <= N)
delete from my_table where rowid in (
select id from (
select rowid id from table_name order by time desc)
where rownum<=n
)