SQL Group By and Order -- retrieve detail for most recent entries in table

It looks like your id values go up with time. That is, it looks like newer entries in your table have higher id values than older entries. If this is true,

SELECT bot_id, MAX(id) id
FROM t_request_history
GROUP BY bot_id

gets you what you want.

If the id values don't go up with time, you have to use a subquery to find the latest time for each bot_id.

                 SELECT bot_id, MAX(request_time) request_time
                   FROM t_request_history
                  GROUP BY bot_id

Then you join that subquery to your table like this:

SELECT a.bot_id, a.id
  FROM t_request_history a
  JOIN (
                    SELECT bot_id, MAX(request_time) request_time
                      FROM t_request_history
                     GROUP BY bot_id
       ) b   ON a.bot_id = b.bot_id
            AND a.request_time = b.request_time

The ON condition of the JOIN chooses just the rows with the latest times from your table.

You could do this using a Window/Analytic function

SELECT distinct
 bot_id, MAX(request_time) OVER(PARTITION BY bot_id)
FROM t_request_history
;

SQLFiddle

You could also find more details on the usage @ MariaDB WindowFunction Max documentation