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

Interesting properties of cross join - sql, Interesting properties of CROSS...

Interesting properties of CROSS JOIN - SQL Compare these with the "interesting properties of JOIN", CROSS JOIN is associative but not commutative. Unlike JOIN and NATURAL JOI

Parameter and keyword description - exit statement, Parameter and Keyword D...

Parameter and Keyword Description: EXIT: An unconditional EXIT statement (i.e., one without a WHEN clause) exits the present loop instantly. The Execution resumes with th

Recursion versus iteration, Recursion versus Iteration Dissimilar the i...

Recursion versus Iteration Dissimilar the iteration, recursion is not crucial to PL/SQL programming. Any problem which can be solved using recursion can be solving using the it

Update the Status of an Ordere, Create a procedure named STATUS_SHIP_SP tha...

Create a procedure named STATUS_SHIP_SP that allows a company to employee in the Shipping Department to update the status of an order to add shipping information. The BB_BASKETSTAT

Pl/sql expressions , Pl/SQL Expressions The Expressions are constructed...

Pl/SQL Expressions The Expressions are constructed by using the operands and operators. An operand is a constant, literal, variable, or function call which contributes a value

Package body, The Package Body The package specification is implemented...

The Package Body The package specification is implemented by the package body. That is, the package body has the definition of every cursor and the subprogram declared in the p

Explicitly specifying the join condition - sql, Explicitly specifying the j...

Explicitly specifying the join condition - SQL SELECT * FROM IS_CALLED JOIN IS_ENROLLED_ON ON ( IS_CALLED.StudentId = IS_ENROLLED_ON.StudentId ) Now, the key word JO

Product-specific packages, Product-specific Packages The Oracle and dif...

Product-specific Packages The Oracle and different Oracle tools are supplied with the product-specific packages which help you to build the PL/SQL-based applications. For illus

Maintain an audit trail of product table changes, The accuracy of product t...

The accuracy of product table data is critical and the Brwebean's. owner wants to have an audit file that contains information regarding all DML activity on the BB_PRODUCT table. T

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