我的表在特定列中有重复的行值。我要删除这些行并保留具有最新id的行。我要检查和比较的列包括：

sub_id, spec_id, ex_time

所以，这张table

+----+--------+---------+---------+-------+
| id | sub_id | spec_id | ex_time | count |
+----+--------+---------+---------+-------+
|  1 |    100 |     444 | 09:29   |     2 |
|  2 |    101 |     555 | 10:01   |    10 |
|  3 |    100 |     444 | 09:29   |    23 |
|  4 |    200 |     321 | 05:15   |     5 |
|  5 |    100 |     444 | 09:29   |     8 |
|  6 |    101 |     555 | 10:01   |     1 |
+----+--------+---------+---------+-------+

我想得到这个结果

+----+--------+---------+---------+-------+
| id | sub_id | spec_id | ex_time | count |
+----+--------+---------+---------+-------+
|  5 |    100 |     444 | 09:29   |     8 |
|  6 |    101 |     555 | 10:01   |     1 |
+----+--------+---------+---------+-------+

根据这个问题，我能够构建这个查询来从多个列中选择所有重复的行

select  t.*
from mytable t join
     (select id, sub_id, spec_id, ex_time, count(*) as NumDuplicates
      from mytable
      group by sub_id, spec_id, ex_time
      having NumDuplicates > 1
     ) tsum
     on t.sub_id = tsum.sub_id and t.spec_id = tsum.spec_id and t.ex_time = tsum.ex_time

但是现在我不知道如何用delete查询 Package 这个select来删除除id最高的行以外的行