Goto statement - sequential control, PL-SQL Programming

GOTO Statement

The GOTO statement branches to a label unconditionally. The label must be exclusive within its scope and should precede an executable statement or a PL/SQL block. If executed, the GOTO statement transfers control to the labeled statement or block. In the following illustration, you go to an executable statement farther down in a series of statements:


BEGIN
...
GOTO insert_row;
...
<>
INSERT INTO emp VALUES...
END;


In the next illustration, you go to a PL/SQL block farther up in a series of statements:


BEGIN
...
<>
BEGIN
UPDATE emp SET ...
...
END;
...
GOTO update_row;
...
END;


The label end_loop in the example below is illegal as it does not precede an executable statement:


DECLARE
done BOOLEAN;
BEGIN
...
FOR i IN 1..50 LOOP
IF done THEN
GOTO end_loop;
END IF;
...

<> -- illegal
END LOOP; -- not an executable statement
END;


To debug the last illustration, now add the NULL statement, as shown:

FOR i IN 1..50 LOOP
IF done THEN
GOTO end_loop;
END IF;
...
<>
NULL; -- an executable statement
END LOOP;


As the following illustration shows, a GOTO statement can branch to an enclosing block from the present block:

DECLARE
my_ename CHAR(10);
BEGIN
<>
SELECT ename INTO my_ename FROM emp WHERE...
BEGIN
...
GOTO get_name; -- branch to enclosing block
END;
END;



Restrictions

Some likely destinations of a GOTO statement are illegal. Particularly, a GOTO statement cannot branch into an IF statement, LOOP statement, or sub-block. For illustration, the following GOTO statement is illegal:



BEGIN
...
GOTO update_row; -- illegal branch into IF statement
...
IF valid THEN
...
<>
UPDATE emp SET...
END IF;
END;

A GOTO statement also cannot branch from one IF statement clause to another, as the following illustration shows:


BEGIN
...
IF valid THEN
...
GOTO update_row; -- illegal branch into ELSE clause
ELSE
...
<>
UPDATE emp SET...
END IF;
END;


The next illustration shows that a GOTO statement cannot branch from an enclose block into a sub-block:


BEGIN
...
IF status = ’OBSOLETE’ THEN
GOTO delete_part; -- illegal branch into sub-block
END IF;
...

BEGIN
...
<>
DELETE FROM parts WHERE...
END;
END;


A GOTO statement also cannot branch out of a subprogram, as the following illustration shows:


DECLARE
...
PROCEDURE compute_bonus (emp_id NUMBER) IS
BEGIN
...
GOTO update_row; -- illegal branch out of subprogram
END;
BEGIN
...
<>
UPDATE emp SET...
END;


Finally, the GOTO statement cannot branch from an exception handler into the present block. For illustration, the following GOTO statement is illegal:


DECLARE
...
pe_ratio REAL;
BEGIN
...
SELECT price / NVL(earnings, 0) INTO pe_ratio FROM ...
<>
INSERT INTO stats VALUES (pe_ratio, ...);
EXCEPTION
WHEN ZERO_DIVIDE THEN
pe_ratio := 0;
GOTO insert_row; -- illegal branch into current block
END;


Though, a GOTO statement can branch from an exception handler into the enclosing block.

Posted Date: 10/3/2012 6:22:19 AM | Location : United States







Related Discussions:- Goto statement - sequential control, Assignment Help, Ask Question on Goto statement - sequential control, Get Answer, Expert's Help, Goto statement - sequential control Discussions

Write discussion on Goto statement - sequential control
Your posts are moderated
Related Questions
DELETE Statement The DELETE statement eliminates whole rows of data from the specified table or view. Syntax:

Control Structures The Control structures are the most important PL/SQL extension to the SQL. Not only does PL/SQL let you manipulate Oracle data, it lets you process the data

Restriction in SQL Syntax: SELECT DISTINCT StudentId FROM IS_CALLED WHERE Name = 'Boris' The WHERE clause operates on the result of the FROM clause in analogo

Named Notation The second procedure call uses the named notation. An arrow (=>) serve as the relationship operator that associates the formal parameter to the left of the arro

Create a view named CustomerAddresses that shows the shipping and billing addresses for each customer in the MyGuitarShop database. This view should return these columns from the

IS NULL Operator The IS NULL operator returns the Boolean value TRUE whenever its operand is null or FALSE if it is not null. The comparisons including the nulls always yield NU

Procedural Constraint Enforcement (Triggers) SQL has an alternative method of addressing database integrity, involving event-driven procedural code. The special procedures th

3CX PBX sync Windows Service Project Description: !! You require access to a commercial version of the 3CX PBX system in order to be able to program the API !! !! You requ

Project Description: We organize an online system called ACPAS we have created a project called EVO that can be use by our customers to integrate their web sites with the Acpas

(a) What are decision support systems, and what role do they play in the business environment? (b) Data warehousing is defined as "a subject-oriented, integrated, non-volatile c