索引优化系列十五--组合查询和in有关的优化

drop table t purge;

create table t as select * from dba_objects;

update t set object_id=rownum ;

create index idx_id_type on t(object_id,object_type);

UPDATE t SET OBJECT_ID=20 WHERE ROWNUM<=26000;

UPDATE t SET OBJECT_ID=21 WHERE OBJECT_ID<>20;

COMMIT;

set linesize 1000

set pagesize 1

alter session set statistics_level=all ;

select /*+index(t,idx1_object_id)*/ * from t where object_TYPE='TABLE' AND OBJECT_ID >= 20 AND OBJECT_ID<= 21;

select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));

--------------------------------------------------------------------------------------------------------

| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |

--------------------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 1 | | 2939 |00:00:00.02 | 1117 |

| 1 | TABLE ACCESS BY INDEX ROWID| T | 1 | 3411 | 2939 |00:00:00.02 | 1117 |

|* 2 | INDEX RANGE SCAN | IDX_ID_TYPE | 1 | 299 | 2939 |00:00:00.02 | 736 |

--------------------------------------------------------------------------------------------------------

2 - access("OBJECT_ID">=20 AND "OBJECT_TYPE"='TABLE' AND "OBJECT_ID"<=21)

filter("OBJECT_TYPE"='TABLE')

已选择25行。

select /*+index(t,idx_id_type)*/ * from t t where object_TYPE='TABLE' AND OBJECT_ID IN (20,21);

select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));

---------------------------------------------------------------------------------------------------------

| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |

---------------------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 1 | | 2939 |00:00:00.01 | 598 |

| 1 | INLIST ITERATOR | | 1 | | 2939 |00:00:00.01 | 598 |

| 2 | TABLE ACCESS BY INDEX ROWID| T | 2 | 3411 | 2939 |00:00:00.01 | 598 |

|* 3 | INDEX RANGE SCAN | IDX_ID_TYPE | 2 | 1 | 2939 |00:00:00.01 | 217 |

---------------------------------------------------------------------------------------------------------

3 - access((("OBJECT_ID"=20 OR "OBJECT_ID"=21)) AND "OBJECT_TYPE"='TABLE')

已选择25行。

---col1,col2,col3的索引情况，如果没有为COL2赋予查询条件时，COL3只能起到检验作用(依然是in的优化）

drop table t purge;

create table t as select * from dba_objects;

UPDATE t SET OBJECT_ID=20 WHERE ROWNUM<=26000;

UPDATE t SET OBJECT_ID=21 WHERE OBJECT_ID<>20;

Update t set object_id=22 where rownum<=10000;

COMMIT;

create index idx_union on t(object_type,object_id,owner);

set autotrace off

alter session set statistics_level=all ;

set linesize 1000

select * from t where object_type='VIEW' and OWNER='LJB';

select * from table(dbms_xplan.display_cursor(null,null,'allstats last'));

------------------------------------------------------------------------------------------------------------

| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads |

------------------------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 24 | 19 |

| 1 | TABLE ACCESS BY INDEX ROWID| T | 1 | 9 | 4 |00:00:00.01 | 24 | 19 |

|* 2 | INDEX RANGE SCAN | IDX_UNION | 1 | 22 | 4 |00:00:00.01 | 21 | 19 |

------------------------------------------------------------------------------------------------------------

select /*+INDEX(T,idx_union)*/ * from t T where object_type='VIEW' and OBJECT_ID IN (20,21,22) AND OWNER='LJB';

----------------------------------------------------------------------------------------------------

| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers |

----------------------------------------------------------------------------------------------------

| 0 | SELECT STATEMENT | | 1 | | 4 |00:00:00.01 | 13 |

| 1 | INLIST ITERATOR | | 1 | | 4 |00:00:00.01 | 13 |

| 2 | TABLE ACCESS BY INDEX ROWID| T | 3 | 1 | 4 |00:00:00.01 | 13 |

|* 3 | INDEX RANGE SCAN | IDX_UNION | 3 | 1 | 4 |00:00:00.01 | 10 |

----------------------------------------------------------------------------------------------------

类似

select /*+INDEX(T,idx_union)*/ * from t T where (object_type='VIEW' and OBJECT_ID =20 AND OWNER='LJB')

or (object_type='VIEW' and OBJECT_ID =21 AND OWNER='LJB')

or (object_type='VIEW' and OBJECT_ID =22 AND OWNER='LJB')