oracle的to_number()有字母报错如何解决

oracle的to_number()有字母报错怎么解决？如：select to_number(123) from table正常select to_number(a1

oracle的to_number()有字母报错怎么解决？
如：
select to_number('123') from table 正常
select to_number('a123') from table 报错。

如何能过滤掉a这个字符？

[解决办法]
上面打错了

SQL code

select    to_number   (Translate('a123','1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ','1234567890'))from dual
[解决办法]
SQL codeselect to_number(REGEXP_REPLACE('a123ch','[a-zA-Z/:.]','')) from table;