oracle 创建索引注意：等于等于或者小于等于的列应该在索引字段的最后一个，否则有回表

create table t1 as select * from sys.dba_objects;
select * from t1 where owner='SYS' and OBJECT_TYPE='TABLE' and object_id >= 3000 and object_id <= 6000 ;

--测试1
create index  t1_idx1 on t1(owner,object_id,OBJECT_TYPE);

SQL> select * from t1 where owner='SYS' and OBJECT_TYPE='TABLE' and object_id >= 3000 and object_id <= 6000 ;


Execution Plan
----------------------------------------------------------
Plan hash value: 1009994977

-----------------------------------------------------------------------------------------------
| Id  | Operation                           | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                    |         |     2 |   264 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID BATCHED| T1      |     2 |   264 |     3   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN                  | T1_IDX1 |     2 |       |     2   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("OWNER"='SYS' AND "OBJECT_ID">=3000 AND "OBJECT_TYPE"='TABLE' AND
              "OBJECT_ID"<=6000)
       filter("OBJECT_TYPE"='TABLE')


Statistics
----------------------------------------------------------
         55  recursive calls
        122  db block gets
         71  consistent gets
          7  physical reads
      32080  redo size
       3018  bytes sent via SQL*Net to client
        465  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          3  rows processed


--测试2
drop index t1_idx1;
create index  t1_idx2 on t1(object_id,owner,OBJECT_TYPE);

SQL>  select * from t1 where owner='SYS' and OBJECT_TYPE='TABLE' and object_id >= 3000 and object_id <= 6000 ;


Execution Plan
----------------------------------------------------------
Plan hash value: 26955123

-----------------------------------------------------------------------------------------------
| Id  | Operation                           | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                    |         |     2 |   264 |    15   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID BATCHED| T1      |     2 |   264 |    15   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN                  | T1_IDX2 |     2 |       |    14   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("OBJECT_ID">=3000 AND "OWNER"='SYS' AND "OBJECT_TYPE"='TABLE' AND
              "OBJECT_ID"<=6000)
       filter("OBJECT_TYPE"='TABLE' AND "OWNER"='SYS')


Statistics
----------------------------------------------------------
          5  recursive calls
          0  db block gets
         19  consistent gets
         13  physical reads
        768  redo size
       3018  bytes sent via SQL*Net to client
        466  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          3  rows processed


--测试3
drop index t1_idx2;
create index  t1_idx3 on t1(owner,OBJECT_TYPE,object_id);
SQL>  select * from t1 where owner='SYS' and OBJECT_TYPE='TABLE' and object_id >= 3000 and object_id <= 6000 ;


Execution Plan
----------------------------------------------------------
Plan hash value: 3017946

-----------------------------------------------------------------------------------------------
| Id  | Operation                           | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                    |         |     2 |   264 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID BATCHED| T1      |     2 |   264 |     3   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN                  | T1_IDX3 |     2 |       |     2   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("OWNER"='SYS' AND "OBJECT_TYPE"='TABLE' AND "OBJECT_ID">=3000 AND
              "OBJECT_ID"<=6000)


Statistics
----------------------------------------------------------
          5  recursive calls
          0  db block gets
          7  consistent gets
          1  physical reads
        120  redo size
       3018  bytes sent via SQL*Net to client
        466  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          3  rows processed

SQL>