Why is no_data_found ORA-01403 an exception in Oracle?

But we still need to answer the question of "why is an exception thrown in the case where a SELECT has no data to be retrieved".

I believe this is done because it's a common situation which might otherwise be overlooked. Writing code as though it always expects to find data is a common thing to do, and if we were supposed to put in error checks such as

SELECT <something...>
IF SQLCODE = 100 THEN -- No data found
  <no-data handler>
END IF

it is likely IMHO that the check for SQLCODE = 100 would be skipped frequently. Having an exception raised rams it right up your nose that A) an important condition (no data found) occurred, and B) NO ALLOWANCE WAS MADE FOR THIS. IMO having the PL/SQL engine raise an exception is better than having the program continue merrily on its way under the assumption that data was retrieved when in fact it wasn't, which can lead to all sorts of other-than-merry problems.

Share and enjoy.

The exception block is not needed, you might use it or not, depending on the context.

Here you are actively ignoring the exception (the procedure will return successfully) but most of the time if you're doing a SELECT INTO you want it to fail if it doesn't return a row, consider:

PROCEDURE update_employee_salary (p_empno) IS
   l_salary NUMBER;
BEGIN
   SELECT sal INTO l_salary FROM emp WHERE empno = p_empno FOR UPDATE;
   /* do something with emp data */
END;

Here I want my function to fail if it is called with an empno that doesn't exist in the EMP table. I might catch the exception to raise a meaningful error message (with raise_application_error) but most of the time I'm happy with the ORA-01403.

In general, the only exceptions you should catch are the expected exceptions (i.e. this should not be the standard to catch all ORA-01403, or all exceptions for that matter).