转换为to_date时,为什么此查询失败

Question

此查询运行并且不返回任何行.

SELECT DISTINCT TO_CHAR(START_DATE,'MM/DD/YYYY'),                             
                TO_CHAR(END_DATE,  'MM/DD/YYYY')                              
FROM                                                                          
(                                   
    SELECT START_DATE, END_DATE, END_DATE - START_DATE
    FROM
    (
        SELECT TO_DATE(SUBSTR(B,  1, 10), 'MM/DD/YYYY') START_DATE,               
               TO_DATE(SUBSTR(B, 14, 10), 'MM/DD/YYYY') END_DATE                  
        FROM (SELECT 'test date' b from dual)
    )
    WHERE END_DATE - START_DATE != 6
)

由于转换错误,这个小块无法运行. [1]:ORA-01858:找到了数字所在的非数字字符

SELECT TO_DATE(SUBSTR(B,  1, 10), 'MM/DD/YYYY') START_DATE,               
       TO_DATE(SUBSTR(B, 14, 10), 'MM/DD/YYYY') END_DATE                  
FROM (SELECT 'test date' b from dual)

我的期望是转换错误会导致Oracle异常导致程序失败.有些事我不知道,或者没有正确思考.

有人能指出这个方向的正确方向吗？

谢谢.邪恶.

编辑 - 使用to_date处理NULL的方式不同. Oracle:在to_date中避免使用NULL值

编辑 - 计划

3 SELECT STATEMENT  ALL_ROWS
Cost: 3  Bytes: 0  Cardinality: 1  
Partition #: 0          
    2 FILTER  
    Cost: 0  Bytes: 0  Cardinality: 0  
    Partition #: 0      
        1 FAST DUAL  
        Cost: 2  Bytes: 0  Cardinality: 1  
        Partition #: 0 

编辑 - 我正在运行10克.

Answer 1

好吧,我想出来因为它让我发疯了.如果您将查询简化为:

SELECT START_DATE, END_DATE, END_DATE - START_DATE
FROM
(
    SELECT TO_DATE(SUBSTR(B,  1, 10), 'MM/DD/YYYY') START_DATE,               
           TO_DATE(SUBSTR(B, 14, 10), 'MM/DD/YYYY') END_DATE                  
    FROM (SELECT 'test date' b from dual)
)
WHERE END_DATE - START_DATE != 6

生成的执行计划(在11gR2上)如下所示:

Execution Plan
----------------------------------------------------------
Plan hash value: 4034615273

-----------------------------------------------------------------
| Id  | Operation        | Name | Rows  | Cost (%CPU)| Time     |
-----------------------------------------------------------------
|   0 | SELECT STATEMENT |      |     1 |     2   (0)| 00:00:01 |
|*  1 |  FILTER          |      |       |            |          |
|   2 |   FAST DUAL      |      |     1 |     2   (0)| 00:00:01 |
-----------------------------------------------------------------

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

   1 - filter(TO_DATE(NULL)-TO_DATE('test date','MM/DD/YYYY')<>6)

因此,CBO已确定END_DATE的子字符串为空,因此,to_date也将导致空值.然后,优化器不会评估START_DATE表达式,并且不会遇到无效的数据格式错误.如果执行,您可以看到相同的行为:

SELECT TO_DATE (NULL) - TO_DATE ('test date', 'MM/DD/YYYY') FROM DUAL

它不会失败.