Oracle alter index disable/unusable的区别

  alter index index_name disable,enable针对函数索引。

SQL> create table test as select * from all_objects;

SQL> create index ind_t_object_id on test(object_id) nologging;
SQL> exec dbms_stats.gather_table_stats(user,'test',cascade => true);
SQL> set autotrace traceonly
SQL> select * from test where object_id = 20;
执行计划
----------------------------------------------------------
Plan hash value: 255872589
-----------------------------------------------------------------------------------------------
| Id  | Operation                   | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |                 |     1 |    96 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST            |     1 |    96 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IND_T_OBJECT_ID |     1 |       |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OBJECT_ID"=20)
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          2  consistent gets
          0  physical reads
          0  redo size
        910  bytes sent via SQL*Net to client
        327  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          0  rows processed


SQL> alter index ind_t_object_id disable;
alter index ind_t_object_id disable
*
第 1 行出现错误:
ORA-02243: ALTER INDEX 或 ALTER MATERIALIZED VIEW 选项无效

SQL> alter index ind_t_object_id unusable;
索引已更改。

SQL> select * from test where object_id = 20;
执行计划
----------------------------------------------------------
Plan hash value: 1357081020
--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |     1 |    96 |   168   (1)| 00:00:03 |
|*  1 |  TABLE ACCESS FULL| TEST |     1 |    96 |   168   (1)| 00:00:03 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("OBJECT_ID"=20)
统计信息
----------------------------------------------------------
        237  recursive calls
          0  db block gets
        795  consistent gets
          0  physical reads
          0  redo size
        910  bytes sent via SQL*Net to client
        327  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          5  sorts (memory)
          0  sorts (disk)
          0  rows processed
          
SQL> drop index ind_t_object_id;
索引已删除。


SQL> create index ind_t_object_id on test(to_char(object_id)) nologging;
索引已创建。


SQL> select * from test where to_char(object_id) = '20';
执行计划
----------------------------------------------------------
Plan hash value: 255872589
-----------------------------------------------------------------------------------------------
| Id  | Operation                   | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |                 |   518 | 49728 |    24   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST            |   518 | 49728 |    24   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IND_T_OBJECT_ID |   207 |       |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access(TO_CHAR("OBJECT_ID")='20')
统计信息
----------------------------------------------------------
         24  recursive calls
          0  db block gets
          5  consistent gets
          1  physical reads
          0  redo size
        910  bytes sent via SQL*Net to client
        327  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          0  rows processed


SQL> alter index ind_t_object_id disable;
索引已更改。
SQL> select * from test where to_char(object_id) = '20';
select * from test where to_char(object_id) = '20'
*
第 1 行出现错误:

ORA-30554: 基于函数的索引FWMS4GZ_DEV_DDL.IND_T_OBJECT_ID被禁用

官方文档：

DISABLE Clause:
DISABLE applies only to a function-based index. This clause lets you disable the use of a function-based index. You might want to do so, for example, while working on the body of the function. Afterward you can either rebuild the index or specify another ALTER INDEX statement with the ENABLE keyword.

UNUSABLE Clause:
   UNUSABLE Clause Specify UNUSABLE to mark the index or index partition(s) or index subpartition(s) UNUSABLE. An unusable index must be rebuilt, or dropped and re-created, before it can be used. While one partition is marked UNUSABLE, the other partitions of the index are still valid. You can execute statements that require the index if the statements do not access the unusable partition. You can also split or rename the unusable partition before rebuilding it.