For this scenario, I have also used the REGEXP function to replace the letters(A-Z,a-z) into 9’s like the example mentioned below:
SELECT REGEXP(<column_name>,'[A-Za-z]', '9') AS result
By executing the above query, I was able to replace the alphabets with 9’s. For more information, you can take a look at the [REGEXP](https://community.denodo.com/docs/html/browse/8.0/en/vdp/vql/functions/text_functions/text_functions#regexp) in the Virtual DataPort VQL Guide.
Hope this helps!!