There is no standard isnumeric function in SQL, but both SQL Server and Oracle do have such a function.

In Teiid if the numerical value follows a simple regex pattern, then you could use LIKE_REGEX.  Otherwise you'd have to use a UDF or define a virtual function with exception handling using a cast -

CREATE VIRTUAL FUNCTION isNumeric(p string) RETURNS boolean AS 
begin
  if (p is null)
    return null;
  declare bigdecimal var = cast(p as bigdecimal);
  return true;
exception e

  return false;
end

You can also log an issue to add isnumeric to the standard function library.