This document provides coding guidelines for control structures and flow control in PL/SQL and SQL. It recommends labeling all loops, using a cursor for loop to process cursor results unless using bulk operations, using a numeric for loop to process dense arrays with 1 as the lower boundary and COUNT() as the upper boundary, and using a while loop to process loose arrays. It advises avoiding GOTO statements and using EXIT WHEN instead of IF/THEN/EXIT to exit loops.

1. PL/SQL & SQL
CODING GUIDELINES – PART 6
Larry Nung

2. AGENDA
Control Structures
Flow Control
Reference
Q&A
2

3. CONTROL STRUCTURES
Flow Control

4. 39. NEVER USE GOTO STATEMENTS IN YOUR
CODE.

5. 40. ALWAYS LABEL YOUR LOOPS.

6. GOOD
BEGIN
<<process_employees>>
FOR r_employee IN (SELECT * FROM emp)
LOOP
…
END LOOP process_employees;
END;

7. 41. ALWAYS USE A CURSOR FOR LOOP TO
PROCESS THE COMPLETE CURSOR RESULTS
UNLESS YOU ARE USING BULK OPERATIONS.

8. GOOD
BEGIN
<<read_employees>>
FOR r_employee IN c_employee
LOOP
…
END LOOP read_employees;
END;

9. 42. ALWAYS USE A NUMERIC FOR LOOP TO
PROCESS A DENSE ARRAY.

10. GOOD
BEGIN
<<process_employees>>
FOR i IN 1..t_employees.COUNT()
LOOP
…
END LOOP process_employees;
END;

11. 43. USE 1 AS LOWER BOUNDARY AND COUNT()
AS UPPER BOUNDARY WHEN LOOPING OVER A
DENSE ARRAY.

12. BAD
DECLARE
t_employees t_employee_type := t_employee_type();
BEGIN
<<process_employees>>
FOR i IN t_employees.FIRST()..t_employees.LAST()
LOOP
…
END LOOP process_employees;
END;

13. GOOD
DECLARE
t_employees t_employee_type := t_employee_type();
BEGIN
<<process_employees>>
IF t_employees IS NOT EMPTY
THEN
FOR i IN t_employees.FIRST()..t_employees.LAST()
LOOP
…
END LOOP process_employees;
END IF;
END;

14. GOOD
DECLARE
t_employees t_employee_type := t_employee_type();
BEGIN
<<process_employees>>
FOR i IN 1..t_employees.COUNT()
LOOP
…
END LOOP process_employees;
END;

15. 44. ALWAYS USE A WHILE LOOP TO PROCESS
A LOOSE ARRAY.

16. GOOD
DECLARE
l_index PLS_INTEGER;
BEGIN
l_index := t_employees.FIRST();
<<process_employees>>
WHILE l_index IS NOT NULL
LOOP
…
l_index := t_employees.NEXT(l_index);
END LOOP process_employees;
END;

17. 45. AVOID USING EXIT TO STOP LOOP
PROCESSING UNLESS YOU ARE IN A BASIC
LOOP.

18. 46. ALWAYS USE EXIT WHEN INSTEAD OF
AN IF STATEMENT TO EXIT FROM A LOOP.

19. BAD
BEGIN
<<process_employees>>
LOOP
...
IF
...
THEN
EXIT process_employees;
END IF;
...
END LOOP process_employees;
END;

20. GOOD
BEGIN
<<process_employees>>
LOOP
...
EXIT process_employees WHEN (...);
END LOOP process_employees;
END;

21. 47. TRY TO LABEL YOUR EXIT WHEN
STATEMENTS.

22. GOOD
BEGIN
l_outerlp := 0;
<<outerloop>>
LOOP
l_innerlp := 0;
l_outerlp := NVL(l_outerlp,0) + 1;
<<innerloop>>
LOOP
l_innerlp := NVL(l_innerlp,0) + 1;
DBMS_OUTPUT.PUT_LINE('Outer Loop counter is ' || l_outerlp || ' Inner
Loop counter is ' || l_innerlp);
EXIT outerloop WHEN l_innerlp = 3;
END LOOP innerloop;
END LOOP outerloop;
END;

23. 48. DO NOT USE A CURSOR FOR LOOP TO
CHECK WHETHER A CURSOR RETURNS DATA.

24. BAD
DECLARE
l_employee_found BOOLEAN := FALSE;
…
BEGIN
<<check_employees>>
FOR r_employee IN c_employee
LOOP
l_employee_found := TRUE;
END LOOP check_employees;
END;

25. GOOD
DECLARE
l_employee_found BOOLEAN := FALSE;
…
BEGIN
OPEN c_employee;
FETCH c_employee INTO r_employee;
l_employee_found := c_employee%FOUND;
CLOSE c_emplyoee;
END;

26. 49. AVOID USE OF UNREFERENCED FOR
LOOP INDEXES.

27. 50. AVOID HARD-CODED UPPER OR LOWER
BOUND VALUES WITH FOR LOOPS.

28. REFERENCE
28

29. 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
29

30. Q&A
30

31. QUESTION & ANSWER
31