Scope and visibility- pl/sql, PL-SQL Programming

Assignment Help:

Scope and Visibility

The References to an identifier are resolved according to its visibility and scope. The scope of an identifier is that area of a program unit (subprogram, block, or package) from which you can reference the identifier. An identifier is visible only in the areas from which you can reference the identifier using an unqualified name. The Figure shows the visibility and scope of a variable named x that is declared in an enclosing block, and then re-declared in a sub-block.

The Identifiers declared in a PL/SQL block are considered local to that block and global to all its sub-blocks. If a global identifier is re-declared in a sub-block, both the identifiers remain in the scope. Within the sub-block, though, only the local identifier is visible as you must use a qualified name to reference the global identifier.

Though you cannot declare an identifier twice in the similar block, you can declare the same identifier in two various blocks. The two items represented by the identifier are discrete, and any change in one does not affect the other. Though, a block cannot reference the identifiers declared in other blocks at the similar level as these identifiers are neither global nor local to the block.

 

2006_Scope and Visibility.jpg

 

                                          Figure: Scope and Visibility




The example below describes the scope rules. Note that the identifiers declared in one sub-block cannot be referenced in another sub-block. That is because the block cannot reference the identifiers declared in another blocks nested at similar level.


DECLARE
a CHAR;
b REAL;
BEGIN

-- identifiers available here: a (CHAR), b
DECLARE
a INTEGER;
c REAL;
BEGIN
-- identifiers available here: a (INTEGER), b, c
END;
DECLARE
d REAL;
BEGIN
-- identifiers available here: a (CHAR), b, d
END;
-- identifiers available here: a (CHAR), b
END;


Remember that the global identifiers can be re-declared in a sub-block, in that case the local declaration prevails and the sub-block cannot reference the global identifier unless you use a qualified name. The qualifier can be the label of an enclose block, as the example below shows:


<>
DECLARE
birthdate DATE;
BEGIN
DECLARE
birthdate DATE;
BEGIN
...
IF birthdate = outer.birthdate THEN...


As the next illustration shown below, the qualifier can also be the name of an enclosing subprogram:


PROCEDURE check_credit (...) IS
rating NUMBER;
FUNCTION valid (...) RETURN BOOLEAN IS
rating NUMBER;
BEGIN
...
IF check_credit.rating < 3 THEN...


Though, within the same scope, a label and a subprogram cannot have the similar name.


Related Discussions:- Scope and visibility- pl/sql

Do you know anyone that can do this type of coding or not?, Task 2 [12 mark...

Task 2 [12 marks] Write the package body for the following package specification (the detailed description of each function and procedure is provided in the appendix below). Place

Keyword and parameter description - forall statement, Keyword &Parameter De...

Keyword &Parameter Description: index_name: This is an undeclared identifier which can be referenced only within the FORALL statement and only as the collection subscript

Using lock table, Using LOCK TABLE You use the LOCK TABLE statement to...

Using LOCK TABLE You use the LOCK TABLE statement to lock the whole database tables in the specified lock mode so that you can share or deny the access to them. For illustrati

While-loop - iterative control, WHILE-LOOP The WHILE-LOOP statement rela...

WHILE-LOOP The WHILE-LOOP statement relates a condition with the series of statements enclosed by the keywords LOOP and END LOOP, as shown: WHILE condition LOOP sequence_of_sta

Using forall statement - bulk bind performance improvement, Using the FORAL...

Using the FORALL Statement The keyword FORALL instruct the PL/SQL engine to bulk-bind input collections before sending them all to the SQL engine. Though the FORALL statement

Assignment statement in pl sql, Assignment Statement: The assignment s...

Assignment Statement: The assignment statement sets the present value of the variable, parameter, field, or element. The statement consists of an assignment target followed by

Use triggers to maintain referential integrity, At times, Brewbean's has ch...

At times, Brewbean's has changed the id number for existing products. In the past, they have had to add a new product row with the new id to the BB_PRODUCT table, modify all the co

Exceptions - syntax, Exceptions An exception is the runtime error or wa...

Exceptions An exception is the runtime error or warning condition that can be predefined or user-defined. The Predefined exceptions are raised implicitly through runtime system

Mutual recursion, Mutual Recursion The Subprograms are mutually recursi...

Mutual Recursion The Subprograms are mutually recursive if they directly or indirectly call each other. In the illustration below, the Boolean functions odd & even, that dete

Using commit, Using COMMIT The COMMIT statements end the present trans...

Using COMMIT The COMMIT statements end the present transaction and make permanent any changes made during that transaction. Till you commit the changes, other users cannot acc

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd