如何创建为单个分区创建索引
设想有一个分区表，上面建了一个local index，如果只是想在最近的分区上使用索引，而老的分区上不需要创建索引，这样的功能只有在12c中提供，而此时就可以使用这个unusable特性，先创建local索引并将其状态置为unusable，然后将需要使用的索引分区进行rebuild，从而实现了针对单个分区创建索引的目的。
SQL> CREATE TABLE INV_HISTORY
2 (inv_no NUMBER(10), inv_date DATE, inv_amt NUMBER(10,2))
3 partition by range (inv_date) interval(numtoyminterval(1,'month'))
4 (partition p0 values less than (to_date('01-01-2005','dd-mm-yyyy')),
5 partition p1 values less than (to_date('01-01-2006','dd-mm-yyyy'))
6 );
Table created.
SQL> insert into inv_history select rownum,to_date('2005-01-01','yyyy-mm-dd'),1000 from dual connect by level<=200000;
200000 rows created.
SQL> /
200000 rows created.
SQL> insert into inv_history select rownum,to_date('2004-01-01','yyyy-mm-dd'),1000 from dual connect by level<=200000;
200000 rows created.
SQL> /
200000 rows created.
SQL> commit;
Commit complete.
SQL> select count(*) from INV_HISTORY partition(p0);
COUNT(*)
----------
400000
SQL> select count(*) from INV_HISTORY partition(p1);
COUNT(*)
----------
400000
SQL> select segment_name,segment_type,partition_name,bytes/1024/1024 from user_segments;
SEGMENT_NAME SEGMENT_TYPE PARTITION_NAME BYTES/1024/1024
------------------------------ ------------------ ------------------------------ ---------------
INV_HISTORY TABLE PARTITION P0 10
INV_HISTORY TABLE PARTITION P1 11
--创建索引并设置为unusable
SQL> CREATE INDEX inv_no_ix ON INV_HISTORY(inv_no) LOCAL unusable;
Index created.
--查看segment情况，发现unusable的索引没有创建segment
SQL> select segment_name,segment_type,partition_name,bytes/1024/1024 from user_segments;
SEGMENT_NAME SEGMENT_TYPE PARTITION_NAME BYTES/1024/1024
------------------------------ ------------------ ------------------------------ ---------------
INV_HISTORY TABLE PARTITION P0 10
INV_HISTORY TABLE PARTITION P1 11
--此时可以对一个索引进行rebuild，rebuild之后该索引将变为usable状态
SQL> alter index INV_NO_IX rebuild partition p1;
Index altered.
SQL> select segment_name,segment_type,partition_name,bytes/1024/1024 from user_segments;
SEGMENT_NAME SEGMENT_TYPE PARTITION_NAME BYTES/1024/1024
------------------------------ ------------------ ------------------------------ ---------------
INV_HISTORY TABLE PARTITION P0 10
INV_HISTORY TABLE PARTITION P1 11
INV_NO_IX INDEX PARTITION P1 8
SQL> select index_name,partition_name,status from user_ind_partitions ;
INDEX_NAME PARTITION_NAME STATUS
------------------------------ ------------------------------ --------
INV_NO_IX P1 USABLE
INV_NO_IX P0 UNUSABLE
--此时如果通过inv_no查询分区p1，则会使用索引
SQL> select * from inv_history where inv_date=to_date('2005-01-01','yyyy-mm-dd') and inv_no=1;
INV_NO INV_DATE INV_AMT
---------- --------- ----------
1 01-JAN-05 1000
1 01-JAN-05 1000
Execution Plan
----------------------------------------------------------
Plan hash value: 2903314601
------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 32 | 5 (0)| 00:00:01 | | |
| 1 | PARTITION RANGE SINGLE | | 2 | 32 | 5 (0)| 00:00:01 | 2 | 2 |
|* 2 | TABLE ACCESS BY LOCAL INDEX ROWID| INV_HISTORY | 2 | 32 | 5 (0)| 00:00:01 | 2 | 2 |
|* 3 | INDEX RANGE SCAN | INV_NO_IX | 2 | | 3 (0)| 00:00:01 | 2 | 2 |
------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("INV_DATE"=TO_DATE(' 2005-01-01 00:00:00', 'syyyy-mm-dd hh24:mi:ss'))
3 - access("INV_NO"=1)
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
6 consistent gets
2 physical reads
0 redo size
739 bytes sent via SQL*Net to client
519 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
2 rows processed
--而查询partition p0时，由于相应的索引分区为unusable状态，不会使用索引，但不影响查询
SQL> select * from inv_history where inv_date=to_date('2004-01-01','yyyy-mm-dd') and inv_no=1;
INV_NO INV_DATE INV_AMT
---------- --------- ----------
1 01-JAN-04 1000
1 01-JAN-04 1000
Execution Plan
----------------------------------------------------------
Plan hash value: 3216071522
------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 32 | 347 (2)| 00:00:05 | | |
| 1 | PARTITION RANGE SINGLE| | 2 | 32 | 347 (2)| 00:00:05 | 1 | 1 |
|* 2 | TABLE ACCESS FULL | INV_HISTORY | 2 | 32 | 347 (2)| 00:00:05 | 1 | 1 |
------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("INV_NO"=1 AND "INV_DATE"=TO_DATE(' 2004-01-01 00:00:00', 'syyyy-mm-dd
hh24:mi:ss'))
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
1213 consistent gets
0 physical reads
0 redo size
739 bytes sent via SQL*Net to client
519 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
2 rows processed
--如果再次将partition p1设置为unusable，那么该分区索引对应的段将被删除
SQL> alter index INV_NO_IX modify partition p1 unusable;
Index altered.
SQL> select index_name,partition_name,status from user_ind_partitions ;
INDEX_NAME PARTITION_NAME STATUS
------------------------------ ------------------------------ --------
INV_NO_IX P1 UNUSABLE
INV_NO_IX P0 UNUSABLE
SQL> select segment_name,segment_type,partition_name,bytes/1024/1024 from user_segments;
SEGMENT_NAME SEGMENT_TYPE PARTITION_NAME BYTES/1024/1024
------------------------------ ------------------ ------------------------------ ---------------
TEST TABLE 3
INV_HISTORY TABLE PARTITION P0 10
INV_HISTORY TABLE PARTITION P1