SELECT COUNT(DISTINCT t1.user)
FROM `table` t1
WHERE NOT EXISTS (   SELECT 1
                     FROM `table t2`
                     WHERE t1.ip=t2.ip
                     AND t1.user != t2.user
                  )

SELECT COUNT(DISTINCT t1.user)
FROM `table` t1
LEFT JOIN `table` t2
     ON t1.ip = t2.ip AND t1.user != t2.user
WHERE t2.user IS NULL

create function getcount()
alter table `table` add column grp;
update `table` set grp=user;
do
    update `table` t1, table t2
    set t1.grp = least(t1.grp, t2.grp), t2.grp = least(t1.grp, t2.grp)
    where t1.ip = t2.ip;
loop until affected_rows()=0;
select @res := count(distinct grp) from `table`;
alter table `table` drop column grp;
return @grp;
end;