to_char()转换多空格的解释

今天在DCBA的blog里看到这篇blog： 

 

 昨天要用SQL来获得一个分区的名称, 却发现生成的分区名中总是多了一个空格, 不知道原因何在, 只是数据库的字符集是UTF8. 如下所示:

18:50:50 SQL> SELECT TO_CHAR(9,'09') FROM DUAL;

TO_
---
 09

    用于获得分区名的语句, 其中9是根据一个公式算出来的值.

18:51:23 SQL> SELECT 'P'||TO_CHAR(9,'09') FROM DUAL;

'P'|
----
P 09

    是显示问题? 不是, DUMP函数显示就是多了一个空格.

18:52:45 SQL> SELECT DUMP(TO_CHAR(9,'09')) coldump from dual;

COLDUMP
----------------------------------------
Typ=1 Len=3: 32,48,57

    还有其他人遇到过吗? 帮忙测试一下? 用Perl或Java程序去执行这个查询, 返回值中一样多了个空格.

 

解释：

SQL> SELECT 'P'||TO_CHAR(9,'FM09') FROM DUAL;

'P'|
----
P09

SQL> SELECT DUMP(TO_CHAR(9,'FM09')) coldump from dual;

COLDUMP
--------------------------------------------------------------------------------
Typ=1 Len=2: 48,57

FM

Fill mode. Oracle uses blank characters to fill format elements to a constant width equal to the largest element for the relevant format model in the current session language. For example, when NLS_LANGUAGE is AMERICAN, the largest element for MONTH is SEPTEMBER, so all values of the MONTH format element are padded to 9 display characters. This modifier suppresses blank padding in the return value of the TO_CHAR function:

In a datetime format element of a TO_CHAR function, this modifier suppresses blanks in subsequent character elements (such as MONTH) and suppresses leading zeroes for subsequent number elements (such as MI) in a date format model. Without FM, the result of a character element is always right padded with blanks to a fixed length, and leading zeroes are always returned for a number element. With FM, which suppresses blank padding, the length of the return value may vary.

In a number format element of a TO_CHAR function, this modifier suppresses blanks added to the left of the number, so that the result is left-justified in the output buffer. Without FM, the result is always right-justified in the buffer, resulting in blank-padding to the left of the number.

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