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今天在選擇一條記錄進行做刪除操作時，碰見index失敗的問題，如下：
處理失敗!錯誤信息:[SQLException  ORA-01502  index  VHL_V6.PK_WEB_APP_TGT_OBJ  or partition of such index is in unusable state ]
在網上查詢了下，知道原因，就上數據庫查了一下，結果如下：
1 PK_WEB_APP_TGT_OBJ NORMAL VHL_V6 TABLE UNUSABLE。
顯然是UNUSABLE狀態，那也就知道原因了，呵呵，解決！

以下為參考文件：

SQL> create table t(a number);
Table created.

1、現在，我們建立一個唯一索引來看看：
SQL> create unique index idx_t on t(a);
Index created.
SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='T';         
no rows selected
SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';
INDEX_NAME                     INDEX_TYPE                  TABLESPACE_NAME                TABLE_TYPE  STATUS
------------------------------ --------------------------- ------------------------------ ----------- --------
IDX_T                          NORMAL                      DATA_DYNAMIC                   TABLE       VALID
SQL> insert into t values(1);
1 row created.
SQL> commit;
Commit complete.

2、將索引手工修改為unusable狀態（模擬發生索引失效的情況）：
SQL> alter index idx_t unusable;
Index altered.
SQL>  select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';
INDEX_NAME                     INDEX_TYPE                  TABLESPACE_NAME                TABLE_TYPE  STATUS
------------------------------ --------------------------- ------------------------------ ----------- --------
IDX_T                          NORMAL                      DATA_DYNAMIC                   TABLE       UNUSABLE
我們看到這是，已經不能正常往表中插入數據：
SQL> insert into t values(2);
insert into t values(2)
*
ERROR at line 1:
ORA-01502: index 'MISC.IDX_T' or partition of sUCh index is in unusable state

3、首先，我們通過重建索引（rebuild index）的方法來解決問題：
SQL> alter index idx_t rebuild;
Index altered.
SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';
INDEX_NAME                     INDEX_TYPE                  TABLESPACE_NAME                TABLE_TYPE  STATUS
------------------------------ --------------------------- ------------------------------ ----------- --------
IDX_T                          NORMAL                      DATA_DYNAMIC                   TABLE       VALID
SQL> insert into t values(2);
1 row created.
SQL> commit;
Commit complete.
SQL>

4、現在我們再次模擬索引失效(unusable狀態)：
SQL> alter index idx_t unusable;
Index altered.
SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';
INDEX_NAME                     INDEX_TYPE                  TABLESPACE_NAME                TABLE_TYPE  STATUS
------------------------------ --------------------------- ------------------------------ ----------- --------
IDX_T                          NORMAL                      DATA_DYNAMIC                   TABLE       UNUSABLE
SQL> insert into t values(3);
insert into t values(3)
*
ERROR at line 1:
ORA-01502: index 'MISC.IDX_T' or partition of such index is in unusable state

5、然后，看看是否可以通過設置參數skip_unusable_indexes=true來解決問題：
SQL> alter session set skip_unusable_indexes=true;
Session altered.
SQL> insert into t values(3);
insert into t values(3)
*
ERROR at line 1:
ORA-01502: index 'MISC.IDX_T' or partition of such index is in unusable state
SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';
INDEX_NAME                     INDEX_TYPE                  TABLESPACE_NAME                TABLE_TYPE  STATUS
------------------------------ --------------------------- ------------------------------ ----------- --------
IDX_T                          NORMAL                      DATA_DYNAMIC                   TABLE       UNUSABLE
SQL> alter index idx_t rebuild;
Index altered.
SQL> select index_name,index_type,tablespace_name,table_type,status from user_indexes where index_name='IDX_T';
INDEX_NAME                     INDEX_TYPE                  TABLESPACE_NAME                TABLE_TYPE  STATUS
------------------------------ --------------------------- ------------------------------ ----------- --------
IDX_T                          NORMAL                      DATA_DYNAMIC                   TABLE       VALID
SQL> insert into t values(3);
1 row created.
SQL> commit;
Commit complete.
SQL>

總結：對于unique index，通過簡單的設置參數是不能解決問題的，要解決unique index 失效的問題，只能通過重建索引來實現。

資料引用:http://www.knowsky.com/388811.html