ORACLE笔试题：存在表T(a,b,c,d),要根据字段c排序后取第21?30条记录显示，请给出sql

1.select * from (select c.*,rownum as rn from (select * from t order by c desc) c) where rn between 21 and 30; 2.select * from (select * from test order by c desc) x where rownum < 30 minus select * from (select * from test order by c desc)