Returning Only Numeric Data

I frequently get e-mail from folks asking about ways to accomplish things in DB2 and SQL. A recent question I got went something like this:

Is there any option to check whether data “IS NUMERIC” in a DB2 table? We want to examine CHAR data but return only those where the entire data consists only of numbers. For example, can we write a query like this?

SELECT *
FROM TABLENAME
WHERE VAR IS NUMERIC.

The VAR variable is defined as a CHAR(5) column and it will contain data like below.
123aa
2234a
34256
32102
add91

Out of the above 5 records we would want only the 3rd and 4th records to be returned. We tried CAST (VAR as integer), but any other option is there for fetching like above. Please explain

Well, if you try to cast non-numeric data to numeric you will get an error. But you can test the data beforehand - digit by digit - using the SUBSTR function. You’d have to break the VAR column down using SUBSTR to get each individual character and test whether that character is between 0 and 9 – then only if all characters are between 0 and 9 would the result be returned.

Here is what the SQL might look like:

SELECT *
FROM TABLENAME
WHERE SUBSTRING(VAR,1,1) BETWEEN '0' AND '9'
AND SUBSTRING(VAR,2,1) BETWEEN '0' AND '9'
AND SUBSTRING(VAR,3,1) BETWEEN '0' AND '9'
AND SUBSTRING(VAR,4,1) BETWEEN '0' AND '9'
AND SUBSTRING(VAR,5,1) BETWEEN '0' AND '9';

This will return only those rows where every digit in the VAR column is a number between zero and nine.