how do i filter out non-numeric values in a text field in teradata?

The best that I've ever managed is this:

where char2hexint(upper(id_field)) = char2hexint(lower(id_field))

Since upper case characters give a different hex value to lower case ones, this will ensure that you have no alphabetical characters, but will still leave you with underscores, colons and so forth. If this doesn't meet your requirements, you may need to write an UDF.

Starting with TD14 Teradata added some functions, now there are multiple ways, e.g.:

WHERE RTRIM(col, '0123456789') = ''

But the easiest way is TO_NUMBER, which returns NULL for bad data:

TO_NUMBER(col)