oracle pl/sql实现找到前面一个字母，如何写呢

oracle pl/sql实现找到前面一个字母，怎么写呢
就是一个函数，传B，得到A
传C，得到B
传Z，得到Y

怎么实现最简单呢，我现在是一个一个判断的，很多个if语句

[解决办法]
使用ascii得到字符序号
select ascii('a') value from dual
然后减一得到字符
select chr(97) value from dual

组合起来即可.
select chr(ascii('a') - 1) value from dual



[解决办法]

SQL code

select chr(ascii('b') - 1) "value" from dual/*v-a1 row selected.*/select chr(ascii('c') - 1) "value" from dual/*v-b1 row selected.*/select chr(ascii('z') - 1) "value" from dual/*v-y1 row selected.*/
[解决办法]
如果传为A-->前面没字母时怎么显示
[解决办法]
SQL code
查看范围 select ascii('a'), ascii('z'), ascii('A'), ascii('Z') from dual;/**       ASCII('A')    ASCII('Z')    ASCII('A')    ASCII('Z')1    97    122    65    90**/select chr(97), chr(122), chr(65), chr(90) from dual;/**       CHR(97)    CHR(122)    CHR(65)    CHR(90)1    a    z    A    Z**/
[解决办法]
探讨

如果传为A-->前面没字母时怎么显示

[解决办法]
[code=SQL][/code]create or replace function f_change_alph (v_str in varchar2)  return varchar2 is

v_ret varchar2(2);
begin
  select translate(v_str,'ABCDEFGHIJKLMNOPQRSTUVWXYZ','BCDEFGHIJKLMNOPQRSTUVWXYZA') into v_ret from  dual;
 return v_ret;
end f_change_alph;


--test
select f_change_alph('Z') res from  dual;
A

[解决办法]
[Quote=引用:]
[code=SQL][/code]create or replace function f_change_alph (v_str in varchar2) return varchar2 is

v_ret varchar2(2);
begin
 select translate(v_str,'ABCDEFGHIJKLMNOPQRSTUVWXYZ','BCDEFGHIJKLMNOPQRS……
[/Quote]

+1

[解决办法]
SQL code
--将b当作参数传入select decode('b','a','z',chr(ascii('b')-1)) as vaule from dual
[解决办法]
可以使用TRANSLATE()函数，轻松实现。
参考代码：

SQL code
SELECT TRANSLATE(原始字符串, 'bcdefghijklmnopqrstuvwxyzaBCDEFGHIJKLMNOPQRSTUVWXYZA',                              'abcdefghijklmnopqrstuvwxyzaABCDEFGHIJKLMNOPQRSTUVWXYZ');
[解决办法]
translate函数果然牛！！！
[解决办法]
用catch case吧，很好的