在Oracle数据库中，通过create table t as select * from dba_objects;语句创建T表，同时通过create index idx_t_object_id on t(object_id) 创建索引，T表的object_id可以为NULL。请问以下哪些SQL语句会利用到索引返回记录？ABCEF A.select avg(object_id) from t ； B.select count(*) from t where object_id is not null; C.select count(object_id) from t where object_id is not null; D.select count(*) from t; E.select avg(object_id) from t where object_id is not null; F.select count(object_id) from t; 1、由于NULL值不参与运算，所以count(object_id)、avg(object_id) 可以利用索引返回结果; 2、B树索引不存储NULL值，所以select count(*) from 无法利用索引返回结果;