你可以用 max() :

select max(col1 * col2)
from t;

要查找匹配的号码：

select count(*)
from t
where (t.col1 * t.col2) = (select max(t2.col1 * t2.col2) from t t2);

也可以使用窗口功能：

select count(*)
from (select t.*, 
             rank() over (order by col1 * col2 desc) as seqnum
      from t
     ) t
where seqnum = 1;