Select mysql 中带有 group by 子句的日期和时间列的最新记录

Question

I have this table from which I have to select the latest row on the basis of date and time column for each checkpost

I have tried the following queries but not returning the latest data for each checkpost.

SELECT checkpost_id,current_rate,date,time FROM revisionrates 
WHERE date IN (SELECT max(date) FROM revisionrates GROUP BY checkpost_id)

The expected output is

Answer 1

You can use window functions:

select rr.*
from (select rr.*,
             row_number() over (partition by checkpost_id order by date desc, time desc) as seqnum
      from revisionrates rr
     ) rr
where seqnum = 1;

This requires MySQL 8.0. In earlier versions of MySQL, this is a bit trickier, but one method uses tuples

select rr.*
from rr
where (date, time) in (select rr2.date, rr2.time
                       from revisionrates rr2
                       where rr2.checkpoint_id = rr.checkpoint_id
                       order by rr2.date desc, rr2.time desc
                       limit 1
                      );