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) y where rownum < 20 order by 3 desc

二者相比，下边的Minus性能稍差。