--16进制转10进制,用to_number,里面的参数是16进制的数据,且参数用单引号括起  
SQL> select to_number('ff','xx') from dual;  
   
TO_NUMBER('FF','XX')  
--------------------  
                 255  
   
--10进制转16进制,用to_char,里面的参数是10进制的数据,且参数不用单引号括起  
SQL> select to_char(255,'xx') from dual;  
   
TO_CHAR(255,'XX')  
-----------------  
 ff  
   
--如下报错因为要转换的16进制的数据宽度与格式串的xx宽度不一样  
SQL> select to_number('10effff','xx') from dual;  
   
select to_number('10effff','xx') from dual  
   
ORA-01722: 无效数字  
   
--续上,修正二者宽度一致,不再报错  
SQL> select to_number('10effff','xxxxxxx') from dual;  
   
TO_NUMBER('10EFFFF','XXXXXXX')  
------------------------------  
                      17760255  
 

--格式串的宽度>=要转化的数据宽度也可以  
SQL> select to_number('10effff','xxxxxxx') from dual;  
   
TO_NUMBER('10EFFFF','XXXXXXX')  
------------------------------  
                      17760255  
   
SQL> select to_number('e','xxxxxxx') from dual;  
   
TO_NUMBER('E','XXXXXXX')  
------------------------  
                      14