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

Theory of special creation - origin of life, THEO R Y OF SPECIAL CREATION...

THEO R Y OF SPECIAL CREATION - Life originated on the earth due to natural events by the super natural power. The biblical story of creation of world within six days was p

Best practices/Data Warhousing, What are 3 good practices of modeling and/o...

What are 3 good practices of modeling and/or implementing data warehouses?

Database Management, Due to an increase in overhead costs, the buying price...

Due to an increase in overhead costs, the buying price of all items needs to be increased. Management wants to see a report before deciding how much each product will go up. Add to

Full time system administrator, Need Windows and Linux system Administrator...

Need Windows and Linux system Administrator We are seeking a part time system administrator to take care of our servers. Your things to do would add, but not limited to: -

Testing triggers, Demonstrate your knowledge of PL/SQL programming by writi...

Demonstrate your knowledge of PL/SQL programming by writing and thoroughly testing triggers and stored procedures associated with an e-commerce application that provides security l

Execute immediate statement - syntax, EXECUTE IMMEDIATE Statement   Th...

EXECUTE IMMEDIATE Statement   The EXECUTE IMMEDIATE statement prepare (parses) and instantly executes a dynamic SQL statement or an anonymous PL/SQL block. Syntax:

First step at defining type sid in sql, First Step at defining type SID in ...

First Step at defining type SID in SQL CREATE TYPE SID AS ( C VARCHAR(5) ) ; Explanation: TYPE SID announces that a type named SID is being defined to the syst

Usefulness of data type, Usefulness of Data Type In SQL, as in most c...

Usefulness of Data Type In SQL, as in most computer languages, a type can be used for constraining the values that are permitted to be used for some purpose. In particular, i

Max and min operator in sql, MAX and MIN operator in SQL Example: ...

MAX and MIN operator in SQL Example: (SELECT MAX (Mark) FROM EXAM_MARK WHERE StudentId = 'S1') (SELECT MIN (Mark) FROM EXAM_MARK WHERE StudentId = 'S1') Example

Oracle development , Write a stored procedure that accepts the post code in...

Write a stored procedure that accepts the post code in which the customer resides as the input parameter. The procedure should then use an explicit cursor to display comprehensive

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