Mysql删除7天以上的记录，同时为每个device_id保留lasr 1条记录

Question

i have a table with device_id and date time with speed as shown below

 id | device_id |      server_time    | speed
 ---+-----------+---------------------+-------
 1  |     3     | 2019-06-24 13:35:37 |   25
 2  |     2     | 2019-06-22 13:35:37 |   35
 3  |     2     | 2019-06-27 15:15:22 |   23
 4  |     3     | 2019-06-24 13:35:37 |   54
 5  |     1     | 2019-06-20 13:35:37 |   55
 6  |     4     | 2019-06-10 13:35:37 |   34
 7  |     3     | 2019-06-24 13:35:37 |   4
 8  |     1     | 2019-06-21 13:35:37 |   25

i want to delete records older than 7 days but i need to keep at least 1 record for each device_id even its older than 7days.

How can I achieve that with mysql?

Answer 1

You can run a query to get the highest ID as that was the request from your comment , and delete all rows where the time is older than 7 days, and not the highest ID for each group.

Since MySQL can't use a subquery on its own table in update/delete queries, you can use a sub-subquery to fetch all the highest IDs grouped by the device_id .

Replace foo with your actual table-name.

DELETE FROM foo
WHERE server_time < DATE_SUB(NOW(), INTERVAL 7 DAY) 
  AND id NOT IN(SELECT * 
                FROM (SELECT MAX(id) 
                      FROM foo 
                      GROUP BY device_id
                ) AS t)

• Live fiddle at http://sqlfiddle.com/#!9/d6fb4c/1

Answer 2

Use row_number()

delete from 
(
  select *, row_number() over(partition by device_id order by server_time desc) as rn
  from tablename where server_Time>=NOW() - INTERVAL 7 DAY
)A where rn<>1

Answer 3

I would write this as join :

delete t
    from <table> t join
         (select device_id,
                 max(server_time) as max_server_time,
                 max(id) as max_id
          from <table> t2
          group by device_id
         ) t2
         on t.device_id = t2.device_id
    where t.id < t2.max_id and
          t.server_time < t2.max_server_time - interval 7 day;