1、创建测试表并设计测试场景：

--创建测试表
sys@ORCL>create table journal_entries
2 (id_je number(8) ,
3 date_je date not null,
4 balanced number ,
5 constraint indx_ecr_id_je primary key(id_je)
6 );

Table created.
--创建索引
sys@ORCL>create index indx_ecr_date_je_balanced on journal_entries(date_je,balanced);

Index created.

sys@ORCL>create index indx_ecr_balanced_date_je on journal_entries(balanced,date_je);

Index created.

sys@ORCL>create index indx_ecr_balanced on journal_entries(balanced);

Index created.
--插入测试数据
sys@ORCL>insert into journal_entries values(1,sysdate,11);

1 row created.

sys@ORCL>insert into journal_entries values(2,sysdate,21);

1 row created.

sys@ORCL>insert into journal_entries values(3,sysdate,31);

1 row created.

sys@ORCL>insert into journal_entries values(4,sysdate,41);

1 row created.

sys@ORCL>insert into journal_entries values(5,sysdate,51);

1 row created.

sys@ORCL>insert into journal_entries values(6,sysdate,61);

1 row created.

sys@ORCL>insert into journal_entries values(7,sysdate,71);

1 row created.

sys@ORCL>insert into journal_entries values(8,sysdate,81);

1 row created.

sys@ORCL>insert into journal_entries values(9,sysdate,91);

1 row created.

sys@ORCL>commit;

Commit complete.
--收集统计信息
sys@ORCL>exec dbms_stats.gather_table_stats(ownname=>USER,tabname=>'JOURNAL_ENTRIES',cascade=>true);

PL/SQL procedure successfully completed.

设计四个场景进行对比：

Sel1 : Select count(*) from journal_entries;
Sel2 : Select count(1) from journal_entries;
Sel3 : Select count(id_je) from journal_entries;

Sel4 : Select count(balanced) from journal_entries;

1、场景1和场景2等价

For CBO, Sel1 and Sel2 are strictly equivalent