26.读书笔记收获不止Oracle之位图索引即席查询

Drop table t purge;

create table t

(name_id,

gender not null,

location not null,

age_group not null,

data)

selectrownum,decode(ceil(dbms_random.value(0,2)),

1,'m',

2,'f')gender,

ceil(dbms_random.value(1,50)) location,

decode(ceil(dbms_random.value(0,3)),'child','young',

3,'middle_age',

4,'old'),

rpad('*',20,'*')

from dual

connect byrownum<=100000;

1. 无索引进行查询

Set linesize 1000

Set autotrace traceonly

sql> select * from t wheregender='m' and location in (1,10,30) andage_group='child';

656 rows selected.

Execution Plan

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

Plan hash value: 1601196873

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

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

| 0| SELECT STATEMENT | |1013 | 39507 | 171 (1)| 00:00:01 |

|* 1| TABLE ACCESS FULL| T | 1013 | 39507 | 171(1)| 00:00:01 |

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

Predicate Information (identified byoperation id):

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

1- filter("AGE_GROUP"='child' AND "GENDER"='m' AND("LOCATION"=1 OR

"LOCATION"=10 OR"LOCATION"=30))

Statistics

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

1recursive calls

0 dbblock gets

652 consistent gets

0physical reads

0 redosize

16591 bytes sent via sql*Net toclient

1024 bytes received via sql*Netfrom client

45sql*Net roundtrips to/from client

0sorts (memory)

0sorts (disk)

656 rows processed

2. 建立联合索引

建立三个列的联合索引

sql> create index idx_union ont(gender,location,age_group);

Index created.

sql> select * from t where gender='m' and location in (1,30) andage_group='child';

656 rows selected.

Execution Plan

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

Plan hash value: 1601196873

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

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

| 0| SELECT STATEMENT | |680 | 26520 | 171 (1)| 00:00:01 |

|* 1| TABLE ACCESS FULL| T |680 | 26520 | 171 (1)| 00:00:01 |

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

Predicate Information (identified byoperation id):

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

1- filter("AGE_GROUP"='child' AND "GENDER"='m' AND("LOCATION"=1 OR

"LOCATION"=10 OR"LOCATION"=30))

Statistics

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

1recursive calls

0 dbblock gets

652 consistent gets

0physical reads

0 redosize

16591 bytes sent via sql*Net toclient

1024 bytes received via sql*Netfrom client

45sql*Net roundtrips to/from client

0sorts (memory)

0sorts (disk)

656 rows processed

还是走的全表扫描，进行强制走索引如下：

3. 强制走索引

sql> select /*+index(t,idx_union)*/ * from t where gender='m' and location in (1,30) andage_group='child';

656 rows selected.

Execution Plan

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

Plan hash value: 886844991

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

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

| 0| SELECT STATEMENT | | 680 | 26520 | 525(0)| 00:00:01 |

| 1| INLIST ITERATOR | | | | | |

| 2| TABLE ACCESS BY INDEX ROWID BATCHED|T |680 | 26520 | 525 (0)| 00:00:01 |

|* 3| INDEX RANGE SCAN | IDX_UNION | 680 | | 5(0)| 00:00:01 |

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

Predicate Information (identified byoperation id):

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

3- access("GENDER"='m' AND ("LOCATION"=1 OR"LOCATION"=10 OR "LOCATION"=30) AND

"AGE_GROUP"='child')

Statistics

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

1recursive calls

0 dbblock gets

581 consistent gets

6physical reads

0 redosize

36681 bytes sent via sql*Net toclient

1024 bytes received via sql*Netfrom client

45sql*Net roundtrips to/from client

0sorts (memory)

0sorts (disk)

656 rows processed

强制走索引的代价比用全表扫描高很多的。主要集中在回表这个阶段。

4. 位图索引

看看走位图索引

sql> create bitmap index gender_idx ont(gender);

Index created.

sql> create bitmap index location_idx ont(location);

Index created.

sql> create bitmap index age_group_idxon t(age_group);

Index created.

sql> select * from t wheregender='m' and location in (1,30) andage_group='child';

656 rows selected.

Execution Plan

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

Plan hash value: 3416549716

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

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

| 0| SELECT STATEMENT | | 680| 26520 | 118 (0)| 00:00:01 |

| 1| TABLE ACCESS BY INDEX ROWID BATCHED| T | 680| 26520 | 118 (0)| 00:00:01 |

| 2| BITMAP CONVERSION TO ROWIDS | | | | | |

| 3| BITMAP AND | | | | | |

| 4| BITMAP OR | | | | | |

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

Predicate Information (identified byoperation id):

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

5- access("LOCATION"=1)

6- access("LOCATION"=10)

7- access("LOCATION"=30)

8- access("AGE_GROUP"='child')

9- access("GENDER"='m')

Statistics

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

1recursive calls

0 dbblock gets

443 consistent gets

5physical reads

0 redosize

36681 bytes sent via sql*Net toclient

1024 bytes received via sql*Netfrom client

45sql*Net roundtrips to/from client

0sorts (memory)

0sorts (disk)

656 rows processed

代价只有118，比全表扫描代价要小很多。

原文链接：https://www.f2er.com/oracle/207061.html

26.读书笔记收获不止Oracle之 位图索引即席查询

1. 无索引进行查询

2. 建立联合索引

3. 强制走索引

4. 位图索引

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26.读书笔记收获不止Oracle之位图索引即席查询