CREATE OR REPLACE FUNCTION is_alphanumeric (string IN VARCHAR2) RETURN BOOLEAN
/*
|| Function tests for ALPHANUMERIC characters, if A-Z or a-z or 0-9 does NOT appear in the string then
||      FALSE is returned.
*/
IS
   i     NUMBER;
 v_boolean  BOOLEAN DEFAULT TRUE;
BEGIN
 FOR i in 1 .. length(string)
 LOOP
  IF  ascii(substr(string,i,1)) between ascii('A') and ascii('Z') THEN
      v_boolean := TRUE;
  ELSIF
      ascii(substr(string,i,1)) between ascii('a') and ascii('z') THEN
      v_boolean := TRUE;
  ELSIF
   ascii(substr(string,i,1)) between ascii('0') and ascii('9') THEN
      v_boolean := TRUE;
  ELSE
   v_boolean := FALSE;
   EXIT;
  END IF;
 END LOOP;
 RETURN(v_boolean);
END;
/