sql - TO_CHAR函数逻辑<<数字格式>>

Question

我是 Oracle 新手，发现有些东西很难理解。尽管我了解 TO_CHAR 的功能，但我对数字格式模型的概念很陌生。请帮我理解下面的逻辑。

select TRIM(substr(TO_CHAR (160, '000'),1,3)) from dual;
Output -> 16

select TRIM(substr(TO_CHAR (160),1,3)) from dual;
Output -> 160

For the 1st query why has the oracle returned the value 16 rather than 160?

Answer 1

以 FM 开头的格式字符串，例如“FM000”。
如果没有 FM，前面会保留一个空格作为减号。

select  '|' || to_char(160,'000')   || '|'     as no_FM
       ,'|' || to_char(160,'FM000') || '|'     as with_FM

from    dual

---

+--------+---------+
| NO_FM  | WITH_FM |
+--------+---------+
| | 160| | |160|   |
+--------+---------+