SQL Server's isNumeric() equivalent in amazon redshift

Question

• I\'m using amazon redshift as my data warehouse
• I have a field (field1)of type string. Some of the strings start with four numbers and others with letters:

Answer 1

Although long time has passed since this question was asked I have not found an adequate response. So I feel obliged to share my solution which works fine on my Redshift cluster today (March 2016).

The UDF function is:

create or replace function isnumeric (aval VARCHAR(20000))
  returns bool
IMMUTABLE 
as $$
    try:
       x = int(aval);
    except:
       return (1==2);
    else:
       return (1==1);
$$ language plpythonu;

Usage would be:

select isnumeric(mycolumn), * from mytable
    where isnumeric(mycolumn)=false