SQL> variable b1 number
SQL> exec :b1 :=3;

PL/SQL procedure successfully completed.

SQL> select * from factor where object_id=:b1;

当使用绑定变量时CBO计算cardicary时使用 rows为table的5%

4983185%5=2500左右

SQL> select count(*) from factor;

  COUNT(*)
----------
     49831

 exec :b1 :=900

SQL> select * from factor where object_id<:b1;

853 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 4037279301

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

| Id  | Operation                   | Name   | Rows  | Bytes | Cost (%CPU)| Time
     |

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

|   0 | SELECT STATEMENT            |        |  2492 |   226K|    12   (0)| 00:0
0:01 |

|   1 |  TABLE ACCESS BY INDEX ROWID| FACTOR |  2492 |   226K|    12   (0)| 00:0
0:01 |

|*  2 |   INDEX RANGE SCAN          | FACIDX |   448 |       |     2   (0)| 00:0
0:01 |

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

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

   2 - access("OBJECT_ID"

Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
        128  consistent gets
          0  physical reads
          0  redo size
      81683  bytes sent via SQL*Net to client
       1001  bytes received via SQL*Net from client
         58  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
        853  rows processed

SQL> select * from factor where object_id<900;

853 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 4037279301

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

| Id  | Operation                   | Name   | Rows  | Bytes | Cost (%CPU)| Time
     |

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

|   0 | SELECT STATEMENT            |        |   860 | 79980 |    22   (0)| 00:0
0:01 |

|   1 |  TABLE ACCESS BY INDEX ROWID| FACTOR |   860 | 79980 |    22   (0)| 00:0
0:01 |

|*  2 |   INDEX RANGE SCAN          | FACIDX |   860 |       |     3   (0)| 00:0
0:01 |

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

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

   2 - access("OBJECT_ID"<900)

Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
        128  consistent gets
          0  physical reads
          0  redo size
      81683  bytes sent via SQL*Net to client
       1001  bytes received via SQL*Net from client
         58  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
        853  rows processed

SQL>