MySQL 백분율 구하기

select  truncate(( b.cnt / a.cnt * 100 ), 2)  cnt , b.fildname from 
( select count(*) cnt from tablename  where fildname <> '') a ,
( select count(fildname) cnt, fildname from tablename  where fildname <> '' group by fildname) b

소숫점 2자리 까지.