how to get distinct rows with max value

Question

my apologies for asking what must be very simple to solve, but I just can\'t seem to wrap my mind around this.. I couldn\'t even come up with a really fitting title for my q

Answer 1

select * from (select * from answers order by votes desc) as temp group by authorId

Answer 2

Great question, Dan.

MySQL lacks the analytical functions to make this easy to solve. A similar question has been asked of Oracle and was solved using the OVER clause with the MAX function. This works on SQL Server too.

You need to use subqueries to do it on MySQL. This works for me:

SELECT
  id,
  authorId,
  answer,
  votes
FROM answers AS firsts
WHERE id = (
  SELECT
    MIN(id)
  FROM answers AS favorites
  WHERE
    votes = (
      SELECT MAX(votes)
      FROM answers AS author_max
      WHERE author_max.authorId = favorites.authorID
    ) AND
    favorites.authorId = firsts.authorId 
)
ORDER BY votes DESC;

See my sqlfiddle for an executable example.

Answer 3

You can use a sub-select:

select min(a1.id), a1.authorid, a2.mxvotes
from answers a1
inner join
(
  select authorid, max(votes) mxvotes
  from answers
  group by authorid
) a2
  on a1.authorid = a2.authorid
  and a1.votes = a2.mxvotes
group by a1.authorid, a2.mxvotes
order by mxvotes desc

see SQL Fiddle with Demo

Answer 4

SELECT id, authorId, answer, votes
FROM (  SELECT id, authorId, answer, votes
        FROM answers
        ORDER BY votes DESC) AS h
GROUP BY authorId

This little neat trick is built basing on GROUP BY to retrieve the first row of each case. Usually this is by default ORDER BY id ASC, but through this sub query, the first row in each authorId with the highest votes.

Note: As mentioned by Iain Elder, this solution doesn't work with ONLY_FULL_GROUP_BY active and only works in MySQL. This solution is to a certain extent unsupported due to lack of documentation confirming this behavior. It works well for me and has always worked well for me however.

This method still works on the latest MySQL on sqlfiddle.