Sequential Control Statements

Unlike the IF and LOOP statements, the sequential control statements GOTO and NULL are not crucial to PL/SQL programming.

The GOTO statement, which goes to a specified statement, is seldom needed. Occasionally, it simplifies logic enough to warrant its use.

The NULL statement, which does nothing, can improve readability by making the meaning and action of conditional statements clear.

Topics

GOTO Statement

The GOTO statement transfers control to a label unconditionally. The label must be unique in its scope and must precede an executable statement or a PL/SQL block. When run, the GOTO statement transfers control to the labeled statement or block.

For GOTO statement restrictions, see "GOTO Statement".

Use GOTO statements sparingly—overusing them results in code that is hard to understand and maintain. Do not use a GOTO statement to transfer control from a deeply nested structure to an exception handler. Instead, raise an exception. For information about the PL/SQL exception-handling mechanism, see PL/SQL Error Handling.

The GOTO statement transfers control to the first enclosing block in which the referenced label appears.

NULL Statement

The NULL statement only passes control to the next statement. Some languages refer to such an instruction as a no-op (no operation).

Some uses for the NULL statement are:

To provide a target for a GOTO statement
To improve readability by making the meaning and action of conditional statements clear
To create placeholders and stub subprograms
To show that you are aware of a possibility, but that no action is necessary

Note:

Using the NULL statement might raise an unreachable code warning if warnings are enabled. For information about warnings, see "Compile-Time Warnings".

Example 5-30 NULL Statement Showing No Action

The NULL statement emphasizes that only salespersons receive commissions.

DECLARE
  v_job_id  VARCHAR2(10);
   v_emp_id  NUMBER(6) := 110;
BEGIN
  SELECT job_id INTO v_job_id
  FROM employees
  WHERE employee_id = v_emp_id;
  
  IF v_job_id = 'SA_REP' THEN
    UPDATE employees
    SET commission_pct = commission_pct * 1.2;
  ELSE
    NULL;  -- Employee is not a sales rep
  END IF;
END;
/

Example 5-31 NULL Statement as Placeholder During Subprogram Creation

The NULL statement lets you compile this subprogram and fill in the real body later.

CREATE OR REPLACE PROCEDURE award_bonus (
  emp_id NUMBER,
  bonus NUMBER
) AUTHID DEFINER AS
BEGIN    -- Executable part starts here
  NULL;  -- Placeholder
  -- (raises "unreachable code" if warnings enabled)
END award_bonus;
/

Example 5-32 NULL Statement in ELSE Clause of Simple CASE Statement

The NULL statement shows that you have chosen to take no action for grades other than A, B, C, D, and F.

CREATE OR REPLACE PROCEDURE print_grade (
  grade CHAR
) AUTHID DEFINER AS
BEGIN
  CASE grade
    WHEN 'A' THEN DBMS_OUTPUT.PUT_LINE('Excellent');
    WHEN 'B' THEN DBMS_OUTPUT.PUT_LINE('Very Good');
    WHEN 'C' THEN DBMS_OUTPUT.PUT_LINE('Good');
    WHEN 'D' THEN DBMS_OUTPUT.PUT_LINE('Fair');
    WHEN 'F' THEN DBMS_OUTPUT.PUT_LINE('Poor');
    ELSE NULL;
  END CASE;
END;
/
BEGIN
  print_grade('A');
  print_grade('S');
END;
/

Result:

Excellent