Question

I have a table called votes

vid     stateid     voterid     voteeid
 1         1           1           1
 2         1           2           1
 3         1           3           1
 4         1           4           1
 5         1           5           2
 6         1           6           2
 7         2           7           3
 8         2           8           3
 9         2           9           4

I want to find the maximum number of votes to a person per state.

Select Top 1 voteeid from votes where stateid = 1 group by voteeid order by count(voteeid) desc

This query is capable of finding maximum number of votes to a person in a single state.

I want to find maximum number votes to a person in every state. In short I want a output like this

votes     voteeid
 4            1
 2            3

Can some one point me in a right direction ?

Thanks

Answer 1

You can group by to find the number of votes per state, and use rank to select all top votee’s:

select  stateid
,       voteeid
,       votes
from    (
        select  stateid
        ,       voteeid
        ,       count(*) as votes
        ,       rank() over (partition by stateid order by count(*) desc) 
                    as rn
        from    @votes
        group by
                stateid
        ,       voteeid
        ) cnt
where   rn = 1

Use row_number instead of rank if you don’t want ties.

For MySQL, you can’t use ranking functions, so you have to add an additional query to find the maximum vote per state:

select  cnt.stateid
,       cnt.voteeid
,       cnt.votes
from    (
        select  stateid
        ,       voteeid
        ,       count(*) as votes
        from    @votes
        group by
                stateid
        ,       voteeid
        ) cnt
join    (
        select  stateid
        ,       max(votes) as maxvotes
        from    (
                select  stateid
                ,       voteeid
                ,       count(*) as votes
                from    @votes
                group by
                        stateid
                ,       voteeid
                ) cnt2
        group by
                stateid
        ) filter_max
on      filter_max.stateid = cnt.stateid
        and filter_max.maxvotes = cnt.votes

Example on SO Data