PL/SQL & SQL CODING GUIDELINES – Part 7

1. PL/SQL & SQL
CODING GUIDELINES – PART 7
Larry Nung

2. AGENDA
Exception Handling
Reference
Q&A
2

3. EXCEPTION HANDLING

4. 51. NEVER HANDLE UNNAMED EXCEPTIONS
USING THE ERROR NUMBER.

5. BAD
BEGIN
...
EXCEPTION
WHEN OTHERS
THEN
IF SQLCODE = -2291
THEN
...
END IF;
END;

6. GOOD
DECLARE
e_parent_missing EXCEPTION;
PRAGMA EXCEPTION_INIT(e_parent_missing,-
2291);
...
BEGIN
...
EXCEPTION
WHEN e_parent_missing
THEN
...
END;

7. 52. NEVER ASSIGN PREDEFINED EXCEPTION
NAMES TO USER DEFINED EXCEPTIONS.

8. BAD
DECLARE
no_data_found EXCEPTION;
…
BEGIN
...
EXCEPTION
WHEN no_data_found
THEN
sys.dbms_output.put_line(co_no_data_found);
END;

9. GOOD
DECLARE
empty_value EXCEPTION;
...
BEGIN
...
EXCEPTION
WHEN empty_value
THEN
sys.dbms_output.put_line(co_empty_value);
WHEN no_data_found
THEN
sys.dbms_output.put_line(co_no_data_found);
END;

10. 53. AVOID USE OF WHEN OTHERS CLAUSE IN AN
EXCEPTION SECTION WITHOUT ANY OTHER
SPECIFIC HANDLERS.

11. BAD
EXCEPTION
WHEN OTHERS
THEN
IF SQLCODE = -1
THEN
update_instead (...);
ELSE
err.log;
RAISE;
END IF;

12. GOOD
EXCEPTION
WHEN DUP_VAL_ON_INDEX
THEN
update_instead (...);
WHEN OTHERS
THEN
err.log;
RAISE;

13. 54. AVOID USE OF EXCEPTION_INIT
PRAGMA FOR A -20,NNN ERROR

14. BAD
CREATE OR REPLACE PROCEDURE
check_hiredate (date_in IN DATE)
IS
BEGIN
IF date_in < ADD_MONTHS (SYSDATE, -1 * 12 * 18)
THEN
RAISE_APPLICATION_ERROR ( -20734,
'Employee must be 18 years old.');
END IF;
END check_hiredate;

15. GOOD
CREATE OR REPLACE PROCEDURE
check_hiredate (date_in IN DATE)
IS
BEGIN
IF emp_rules.emp_too_young (date_in)
THEN
err.raise (errnums.emp_too_young);
END IF;
END check_hiredate;

16. 55. AVOID USE OF THE
RAISE_APPLICATION_ERROR BUILT-IN
PROCEDURE WITH A HARD-CODED -
20,NNN ERROR NUMBER OR HARD-CODED
MESSAGE.

17. BAD
BEGIN
raise_application_error(-20501,'Invalid
employee_id');
END;

18. GOOD
BEGIN
err_up.raise(in_error =>
err.co_invalid_employee_id);
END;

19. 56. AVOID UNHANDLED EXCEPTIONS

20. BAD
CREATE OR REPLACE PACKAGE BODY department_api IS
FUNCTION name_by_id (in_id IN
departments.department_id%TYPE)
RETURN departments.department_name%TYPE IS
l_department_name departments.department_name%TYPE;
BEGIN
SELECT department_name
INTO l_department_name
FROM departments
WHERE department_id = in_id;
RETURN l_department_name;
END name_by_id;
END department_api;

21. GOOD
CREATE OR REPLACE PACKAGE BODY department_api IS
FUNCTION name_by_id (in_id IN departments.department_id%TYPE)
RETURN departments.department_name%TYPE IS
l_department_name departments.department_name%TYPE;
BEGIN
SELECT department_name
INTO l_department_name
FROM departments
WHERE department_id = in_id;
RETURN l_department_name;
EXCEPTION
WHEN NO_DATA_FOUND
THEN
RETURN NULL;
WHEN TOO_MANY_ROWS
THEN
RAISE;
END name_by_id;
END department_api;

22. 57. AVOID USING ORACLE’S PREDEFINED
EXCEPTIONS

23. BAD
BEGIN
RAISE NO_DATA_FOUND;
END;

24. GOOD
DECLARE
my_exception EXCEPTION;
BEGIN
RAISE my_exception;
END;

25. REFERENCE
25

26. REFERENCE
 Trivadis PL/SQL & SQL Coding Guidelines Version
2.0
 http://www.trivadis.com/sites/default/files/downloads/PL
SQL_and_SQL_Coding_Guidelines_2_0_HiRes.pdf
26

27. Q&A
27

28. QUESTION & ANSWER
28