select group1, format(sum(c1_mult), 'N') c1, format(max(product_c2), 'N') as c2
  from (select group1, 
               c1*exp(sum(log(c2)) over (partition by group1))/c2 c1_mult,
               exp(sum(log(c2)) over (partition by group1)) product_c2 
          from (values
                  ('1', 1, 2),
                  ('1', 2, 1.4),
                  ('1', 3, 5.2),
                  ('2', 1, 0.6),
                  ('2', 4, 0.5),
                  ('2', 3, 0.9)) as tab1(group1, c1, c2)
        ) as t
 group by group1
 order by group1;