Using ORDER BY and GROUP BY together

One way to do this that correctly uses group by:

select l.* from table linner join (  select     m_id, max(timestamp) as latest   from table   group by m_id) r  on l.timestamp = r.latest and l.m_id = r.m_idorder by timestamp desc

How this works:

• selects the latest timestamp for each distinct m_id in the subquery
• only selects rows from table that match a row from the subquery (this operation -- where a join is performed, but no columns are selected from the second table, it's just used as a filter -- is known as a "semijoin" in case you were curious)
• orders the rows

If you really don't care about which timestamp you'll get and your v_id is always the same for a given m_i you can do the following:

select m_id, v_id, max(timestamp) from tablegroup by m_id, v_idorder by timestamp desc

Now, if the v_id changes for a given m_id then you should do the following

select t1.* from table t1left join table t2 on t1.m_id = t2.m_id and t1.timestamp < t2.timestampwhere t2.timestamp is nullorder by t1.timestamp desc

Here is the simplest solution

select m_id,v_id,max(timestamp) from table group by m_id;

Group by m_id but get max of timestamp for each m_id.