Question

I have the following query which does what I want, but I suspect it is possible to do this without a subquery:

  SELECT * 
    FROM (SELECT * 
            FROM 'versions' 
        ORDER BY 'ID' DESC) AS X 
GROUP BY 'program'

What I need is to group by program, but returning the results for the objects in versions with the highest value of “ID”.

In my past experience, a query like this should work in MySQL, but for some reason, it’s not:

  SELECT * 
    FROM 'versions' 
GROUP BY 'program' 
ORDER BY MAX('ID') DESC

What I want to do is have MySQL do the ORDER BY first and then the GROUP BY, but it insists on doing the GROUP BY first followed by the ORDER BY. i.e. it is sorting the results of the grouping instead of grouping the results of the ordering.

Of course it is not possible to write

SELECT * FROM 'versions' ORDER BY 'ID' DESC GROUP BY 'program'

Thanks.

Answer 1

This should do it and work pretty well as long as there is a composite index on (program,id). The subquery should only inspect the very first id for each program branch, and quickly retrieve the required record from the outer query.

select v.*
from
(
    select program, MAX(id) id
    from versions
    group by program
) m
inner join versions v on m.program=v.program and m.id=v.id