隐式转换引起的索引失效

最新推荐文章于 2025-02-18 16:08:09 发布

congwei1863

最新推荐文章于 2025-02-18 16:08:09 发布

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隐式转换引起的索引失效

SQL> create table test1 (userid varchar2(10));

Table created.

SQL> select * from test1;

no rows selected

SQL> insert into test1 select object_id from dba_objects;

72693 rows created.

SQL> create index id_idx on test1 (userid);

Index created.

SQL> set autotrace trace

SQL> select * from test1 where userid=2; --条件是number类型

Execution Plan
----------------------------------------------------------
Plan hash value: 4122059633

---------------------------------------------------------------------------
| Id | Operation         | Name | Rows | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT |       |     1 |     7 |    33   (4)| 00:00:01 |
|* 1 | TABLE ACCESS FULL| TEST1 |     1 |     7 |    33   (4)| 00:00:01 |
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter(TO_NUMBER("USERID")=2)

Note
-----
- dynamic sampling used for this statement (level=2)

Statistics
----------------------------------------------------------
          1 recursive calls
          0 db block gets
        116 consistent gets
          0 physical reads
          0 redo size
        523 bytes sent via SQL*Net to client
        523 bytes received via SQL*Net from client
          2 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
          1 rows processed

SQL> select * from test1 where userid='2'; --加上引号后变成字符类型

Execution Plan
----------------------------------------------------------
Plan hash value: 1357208269

---------------------------------------------------------------------------
| Id | Operation        | Name   | Rows | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT |        |     1 |     7 |     1   (0)| 00:00:01 |
|* 1 | INDEX RANGE SCAN| ID_IDX |     1 |     7 |     1   (0)| 00:00:01 |
---------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - access("USERID"='2')

Note
-----
- dynamic sampling used for this statement (level=2)

Statistics
----------------------------------------------------------
          0 recursive calls
          0 db block gets
          3 consistent gets
          0 physical reads
          0 redo size
        523 bytes sent via SQL*Net to client
        523 bytes received via SQL*Net from client
          2 SQL*Net roundtrips to/from client
          0 sorts (memory)
          0 sorts (disk)
          1 rows processed

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转载于:http://blog.itpub.net/26655292/viewspace-753368/