Returning the 'last' row of each 'group by' in MySQL

Question

Is there a more efficient way of doing the following?

select * 
    from foo as a
    where a.id = (select max(id) from foo where uid = a.uid group by uid)
          


        

Answer 1

Try this query -

SELECT t1.* FROM foo t1
  JOIN (SELECT uid, MAX(id) id FROM foo GROUP BY uid) t2
    ON t1.id = t2.id AND t1.uid = t2.uid;

Then use EXPLAIN to analyze queries.

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SELECT t1.* FROM foo t1
  LEFT JOIN foo t2
    ON t1.id < t2.id AND t1.uid = t2.uid
WHERE t2.id is NULL;