How I can check a substring is a valid number in postgresql ?

Dear All,

How I can check a substring is a valid number in postgresql ?

example:

I have a query

select max(substring(code,2,length(code))::INT) from emp where
substring(code,0,2) = 'A';

code
========
A0001
A0002
ABC005
S0002

This query fails because of ABC002, how I can avoid this error , if there is
a any way to check substring(code,1,length(code)) is a number ,then i can
correct the query by put it in where condition.

I want to get the result as 2(ie want to avoid checking ABC005

is there is any built in function to check the substring is a number in
postgresql?

Iam using postgres 8.1.8

pls help me

thanks in advance:

Anoop