多选题 在oracle中，排序时NULL值比任何值都大，进行倒序排序时空值会显示在最前面，可以通过下面哪些方法让空值排在最后面？(AB) A. select *from emp order by comm desc nulls last； B. select * from emp order by nvl(comm,TO_BINARY_FLOAT('-INF')) desc C. select * from emp order by nvl(comm,TO_BINARY_FLOAT('INF')) desc; D. select *from emp order by comm desc nulls first;