Oracle之回表消失，不取无用列

drop table t purge;
create table t as select * from dba_objects;
create index idx_object_id on t(object_id,object_type);


set linesize 1000
set autotrace traceonly
select object_id,object_type from t where object_id=28;
/

select * from t where object_id=28;

/

解析：通过执行计划对比，发现少了

TABLE ACCESS BY INDEX ROWID(回表）