Oracle学习笔记索引执行计划中的关键字（十三）

其他 2020-02-19 13:34:10 阅读次数: 0

INDEX RANGE SCAN：索引范围查询

drop table t purge;
create table t as select * from dba_objects;
update t set object_id=rownum;
commit;
create  index idx_object_id on t(object_id);
set autotrace traceonly
set linesize 1000
exec dbms_stats.gather_table_stats(ownname => 'LJB',tabname => 'T',estimate_percent => 10,method_opt=> 'for all indexed columns',cascade=>TRUE) ;  

select * from t where object_id=8;
执行计划
---------------------------------------------------------------------------------------------
| Id  | Operation                   | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |               |     1 |   207 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T             |     1 |   207 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_OBJECT_ID |     1 |       |     1   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          4  consistent gets
          0  physical reads
          0  redo size
       1394  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

　　INDEX UNIQUE SCAN：索引唯一性查询

--请注意这个INDEX UNIQUE SCAN扫描方式,在唯一索引情况下使用。

drop table t purge;
create table t as select * from dba_objects;
update t set object_id=rownum;
commit;
create unique index idx_object_id on t(object_id);
set autotrace traceonly
set linesize 1000

select * from t where object_id=8;
执行计划
---------------------------------------------------------------------------------------------
| Id  | Operation                   | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |               |     1 |   207 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T             |     1 |   207 |     2   (0)| 00:00:01 |
|*  2 |   INDEX UNIQUE SCAN         | IDX_OBJECT_ID |     1 |       |     1   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------|
统计信息
---------------------------------------------------
          0  recursive calls
          0  db block gets
          3  consistent gets
          0  physical reads
          0  redo size
       1298  bytes sent via SQL*Net to client
        404  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

TABLE ACCESS BY USER ROWID：索引rowid查询

--请注意这个TABLE ACCESS BY USER ROWID扫描方式,直接根据rowid来访问，最快的访问方式！

drop table t purge;
create table t as select * from dba_objects;
update t set object_id=rownum;
commit;
--注意，这里连索引都没建!
--create  index idx_object_id on t(object_id);
set autotrace off
select rowid from t where object_id=8; 
ROWID
------------------
AAAZxiAAGAAAB07AAH

set autotrace traceonly
set linesize 1000

select * from t where object_id=8 and rowid='AAAZxiAAGAAAB07AAH';
执行计划
-----------------------------------------------------------------------------------
| Id  | Operation                  | Name | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT           |      |     1 |   219 |     1   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS BY USER ROWID| T    |     1 |   219 |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          1  consistent gets
          0  physical reads
          0  redo size
       1391  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

INDEX FULL SCAN：索引全扫描

---请记住这个INDEX FULL SCAN扫描方式，并体会与INDEX FAST FULL SCAN的区别

drop table t purge;
create table t as select * from dba_objects;
update t set object_id=rownum;
commit;
alter table T modify object_id not null;
create  index idx_object_id on t(object_id);
set autotrace traceonly
set linesize 1000

select * from t  order by object_id;
执行计划
---------------------------------------------------------------------------------------------
| Id  | Operation                   | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |               | 88780 |    17M|  1208   (1)| 00:00:15 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T             | 88780 |    17M|  1208   (1)| 00:00:15 |
|   2 |   INDEX FULL SCAN           | IDX_OBJECT_ID | 88780 |       |   164   (1)| 00:00:02 |
---------------------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
      10873  consistent gets
          0  physical reads
          0  redo size
    8116181  bytes sent via SQL*Net to client
      54040  bytes received via SQL*Net from client
       4877  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      73130  rows processed

INDEX FAST FULL SCAN：索引min和max全扫描

--请注意这个INDEX FULL SCAN (MIN/MAX)扫描方式

drop table t purge;
create table t as select * from dba_objects;
update t set object_id=rownum;
commit;
create  index idx_object_id on t(object_id);
set autotrace traceonly
set linesize 1000

select max(object_id) from t;
执行计划
--------------------------------------------------------------------------------------------
| Id  | Operation                  | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT           |               |     1 |    13 |     2   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE            |               |     1 |    13 |            |          |
|   2 |   INDEX FULL SCAN (MIN/MAX)| IDX_OBJECT_ID |     1 |    13 |     2   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          2  consistent gets
          0  physical reads
          0  redo size
        431  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

INDEX FULL SCAN (MINMAX)：索引快速全扫描

---请记住这个INDEX FAST FULL SCAN扫描方式，并体会与INDEX FULL SCAN的区别

drop table t purge;
create table t as select * from dba_objects ;
update t set object_id=rownum;
commit;
alter table T modify object_id not null;
create  index idx_object_id on t(object_id);
set autotrace traceonly
set linesize 1000

select count(*) from t;
执行计划
-------------------------------------------------------------------------------
| Id  | Operation             | Name          | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |               |     1 |    49   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE       |               |     1 |            |          |
|   2 |   INDEX FAST FULL SCAN| IDX_OBJECT_ID | 88780 |    49   (0)| 00:00:01 |
-------------------------------------------------------------------------------
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
        170  consistent gets
          0  physical reads
          0  redo size
        425  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

INDEX SKIP SCAN：跳跃索引

--请记住这个INDEX SKIP SCAN扫描方式

drop table t purge;
create table t as select * from dba_objects;
update t set object_type='TABLE' ;
commit;
update t set object_type='VIEW' where rownum<=30000;
commit;
create  index idx_type_id on t(object_type,object_id);
exec dbms_stats.gather_table_stats(ownname => 'LJB',tabname => 'T',estimate_percent => 10,method_opt=> 'for all indexed columns',cascade=>TRUE) ;  
set autotrace traceonly
set linesize 1000
select * from t where object_id=8;

执行计划
-------------------------------------------------------------------------------------------
| Id  | Operation                   | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |             |     1 |    94 |     4   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T           |     1 |    94 |     4   (0)| 00:00:01 |
|*  2 |   INDEX SKIP SCAN           | IDX_TYPE_ID |     1 |       |     3   (0)| 00:00:01 |
-------------------------------------------------------------------------------------------

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

   2 - access("OBJECT_ID"=8)
       filter("OBJECT_ID"=8)


统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          7  consistent gets
          0  physical reads
          0  redo size
       1401  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

TABLE ACCESS BY INDEX ROWID：回表

drop table t purge;
create table t as select * from dba_objects;
update t set object_id=rownum;
commit;
create  index idx_object_id on t(object_id);
set autotrace traceonly explain
set linesize 1000

select object_id from t where object_id=2 and object_type='TABLE';
---------------------------------------------------------------------------------------------
| Id  | Operation                   | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |               |     9 |   216 |     2   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS BY INDEX ROWID| T             |     9 |   216 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IDX_OBJECT_ID |    12 |       |     1   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------


TABLE ACCESS BY INDEX ROWID消失了。
create  index idx_id_type on t(object_id,object_type);
select object_id from t where object_id=2 and object_type='TABLE';

执行计划
--------------------------------------------------------------------------------
| Id  | Operation        | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |             |     9 |   216 |     1   (0)| 00:00:01 |
|*  1 |  INDEX RANGE SCAN| IDX_ID_TYPE |     9 |   216 |     1   (0)| 00:00:01 |
--------------------------------------------------------------------------------

　　

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