Finding exception (PL/SQL) - oracle

Question

I am running a code in Oracle that asks the user to input a route type, and then the program fetches the longest and shortest routes depending on the user-input route, as well as the number of rows fetched. I need to add any exception to the code and I am trying to think of what kind of exception I could add in this case. I was thinking of adding an exception that gives an error if the rows fetched is <1. However, I am not sure if such exception exists. I also need to add an exception for an invalid route type. I have represented this as an IF statement. Not sure if this counts as an exception.
My code is:
SET SERVEROUTPUT ON;
SET VERIFY OFF
DECLARE
v_type VARCHAR2 (20);
min_length NUMBER;
max_length NUMBER;
v_count NUMBER;
BEGIN
v_type := '&InsertTypeRoute';
IF v_type = 'Multi-Lane Divided' OR
v_type = 'Paved Divided' OR
v_type = 'Paved Undivided' THEN
SELECT MIN(LENGTH_KM), MAX(LENGTH_KM), COUNT(LENGTH_KM) INTO min_length, max_length, v_count
FROM TBLROUTE WHERE TYPE = v_type;
DBMS_OUTPUT.PUT_LINE('The minimum length is: ' || TO_CHAR(min_length));
DBMS_OUTPUT.PUT_LINE('The maximum length is: ' || TO_CHAR(max_length));
DBMS_OUTPUT.PUT_LINE ('Total number of '|| v_type ||' route is: ' || TO_CHAR(v_count));
ELSE
DBMS_OUTPUT.PUT_LINE ('Route type cannot be found');
END IF;
/*
EXCEPTION
WHEN NO_DATA_FOUND THEN
DBMS_OUTPUT.PUT_LINE ('Route type cannot be found'); */
END;
/
How about these exception? Are they appropriate in this case?
EXCEPTION
WHEN NO_DATA_FOUND THEN
DBMS_OUTPUT.PUT_LINE ('Data not found');
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('This program encountered an error');

Answer 1

It is suggested to add SQLCODE and SQLERRM if you are using WHEN_OTHERS along with RAISE
This will tell you exactly what went wrong.
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('ERROR MESSAGE :' || SQLCODE || ' :' || SQLERRM );
RAISE;

Answer 2

"Are they appropriate in this case?"
Handling exceptions like this is universally accepted as bad practice. It swallows the real exception, so the user knows that something failed but they have absolutely no idea what.
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('This program encountered an error');
Here is a circumstance where doing nothing is better than doing that.
In your situation I suggest you rely on the default PL/SQL NO_DATA_FOUND exception to handle no records, and raise a bespoke exception for when there's only one. Something like this:
DECLARE
v_type VARCHAR2 (20);
min_length NUMBER;
max_length NUMBER;
v_count NUMBER;
-- user-defined exception
x_single_route exception;
pragme expcetion_init(x_single_route, -20001);
BEGIN
v_type := '&InsertTypeRoute';
IF v_type = 'Multi-Lane Divided' OR
v_type = 'Paved Divided' OR
v_type = 'Paved Undivided'
THEN
SELECT MIN(LENGTH_KM), MAX(LENGTH_KM), COUNT(LENGTH_KM) INTO min_length, max_length, v_count
FROM TBLROUTE WHERE TYPE = v_type;
IF v_count > 1 THEN
DBMS_OUTPUT.PUT_LINE('The minimum length is: ' || TO_CHAR(min_length));
DBMS_OUTPUT.PUT_LINE('The maximum length is: ' || TO_CHAR(max_length));
DBMS_OUTPUT.PUT_LINE ('Total number of '|| v_type ||' route is: ' || TO_CHAR(v_count));
ELSE
raise x_single_route;
END IF;
EXCEPTION
WHEN x_single_route THEN
DBMS_OUTPUT.PUT_LINE ('Route has only one leg');
WHEN NO_DATA_FOUND THEN
DBMS_OUTPUT.PUT_LINE ('Route type cannot be found');
END;
/
Generally it is good practice to RAISE exceptions: users want to know when something goes wrong. (Although as this appears to be a user-facing program, so it's slightly different.)
...
EXCEPTION
WHEN x_single_route THEN
DBMS_OUTPUT.PUT_LINE ('Route has only one leg');
RAISE;
WHEN NO_DATA_FOUND THEN
....

Answer 3

You could use the RAISE_APPLICATION_ERROR procedure to raise a particular exception in the user-defined range (-20000..-20999), then define an exception so you can catch it. Something like the following should work:
DECLARE
SOMETHING_UNWANTED_HAPPENS BOOLEAN := TRUE;
BEGIN
IF SOMETHING_UNWANTED_HAPPENS THEN
RAISE_APPLICATION_ERROR(-20001, 'Something I didn''t want happened');
END IF;
EXCEPTION
WHEN OTHERS THEN
IF SQLCODE = -20001 THEN
DBMS_OUTPUT.PUT_LINE('My user-defined exception was raised');
-- Do whatever else you want to do to handle this exception
ELSE
DBMS_OUTPUT.PUT_LINE('Something else happened');
END IF;
END;
Or you could declare an EXCEPTION variable, initialize it with PRAGMA EXCEPTION_INIT, and then use it like any other exception:
DECLARE
my_exception EXCEPTION;
PRAGMA EXCEPTION_INIT(my_exception, -20001);
SOMETHING_UNWANTED_HAPPENS BOOLEAN := TRUE;
BEGIN
IF SOMETHING_UNWANTED_HAPPENS THEN
RAISE my_exception;
END IF;
EXCEPTION
WHEN my_exception THEN
DBMS_OUTPUT.PUT_LINE('My user-defined exception was raised');
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('Something else happened');
END;