Data abstraction, PL-SQL Programming

Data Abstraction

The Data abstraction extracts the important properties of data while ignoring the not necessary details. Once you design a data structure, you can fail to remember the details and focus on designing algorithms that manipulate the data structure.

Collections

The collection types TABLE and VARRAY permit you to declare nested tables and variable-size arrays (varrays in short). A collection is an ordered group of elements, all of the similar type. Every element has a unique subscript that determines its place in the collection.

To reference an element, use the standard subscripting syntax. For e.g., the following call references the 5th element in the nested table returned by the function new_hires:

DECLARE

TYPE Staff IS TABLE OF Employee;

staffer Employee;

FUNCTION new_hires (hiredate DATE) RETURN Staff IS

BEGIN ... END;

BEGIN

staffer := new_hires('10-NOV-98')(5);

...

END;

The Collections work like an array found in most third-generation programming languages. The collections can also be passed as parameters. And hence, you can use them to move columns of data into and out of database tables or between the client-side applications and stored subprograms.

Records

You can use the %ROWTYPE attribute to declare a record that shows a row in a table or a row fetched from a cursor. Although, with a user-defined record, you can declare fields of your own. The Records contain exclusively named fields that can have different datatypes. Assume that you have different data about an employee like name, salary, & hire date. These items are not similar in type but logically related. Records containing a field for each item treat the data as a logical unit. Consider the example shown below:

DECLARE

TYPE TimeRec IS RECORD (hours SMALLINT, minutes SMALLINT);

TYPE MeetingTyp IS RECORD

(

date_held DATE,

duration TimeRec, -- nested record

location VARCHAR2(20),

purpose VARCHAR2(50));

Remember that you can nest the records. That is, the record can be the component of another record.

Posted Date: 10/2/2012 1:49:29 AM | Location : United States







Related Discussions:- Data abstraction, Assignment Help, Ask Question on Data abstraction, Get Answer, Expert's Help, Data abstraction Discussions

Write discussion on Data abstraction
Your posts are moderated
Related Questions
Overloading The PL/SQL overloads the subprogram names. That is, you can use similar name for few different subprograms as long as their formal parameters differ in the number

Parameter and Keyword Description: type_name: This identifies a user-defined type specifier that is used in the subsequent declarations of the objects. AUTHID Clause:

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

DBMS: The answer to this question is of course given in of the theory book. This book is concerned with SQL DBMSs and SQL databases in particular. Soon we will be looking a

Pl/sql Conditional Control: IF statements Frequently, it is necessary to take the alternative actions depending on the circumstances. The IF statement execute a series of statem

Cursor Variables As Parameters You can declare the cursor variables as the formal parameters of the functions and procedures. In the illustration below, you define the REF CUR

UPDATE Command- SQL Loosely speaking, UPDATE changes some of the column values of some existing rows of its target table. Thus, although some rows disappear from the target an

Parameter and Keyword Description: collection_name: This keyword identifies the index-by table, nested table, or varray formerly declared within the present scope. cu

THEO R Y OF CATASTROPHISM OR CATALYSM (CUVIER 1769-1832) - The world has passed thorugh several stages and at the end of each stage there was a catastrophe killing all the

Wrapping and unwrapping in SQL Operators WRAP and UNWRAP in connection with attributes whose declared types are tuple types. Example shows how extension and projection can be