select a.soda, a.person
  from table a
 where not exists(select 1
                   from table b
                  where b.person = a.person
                    and b.soda <> a.soda)

select distinct * from sodas as s1 where s1.name not in (select s2.name from sodas as s2 where s2.name=s1.name and s2.soda <> s1.soda)