Map and order methods, PL-SQL Programming

Map and Order Methods:

The values of the scalar datatype like CHAR or REAL have a predefined order that allows them to be compared. While, the instances of an object type has no predefined order. To put them in order, the PL/SQL calls a map method supplied by you.

In the illustration below, the keyword MAP indicates that the method converts orders rational objects by mapping them to the REAL values:

CREATE TYPE Rational AS OBJECT (

num INTEGER,

den INTEGER,

MAP MEMBER FUNCTION convert RETURN REAL,

...

);

CREATE TYPE BODY Rational AS

MAP MEMBER FUNCTION convert RETURN REAL IS

BEGIN

RETURN num / den;

END convert;

...

END;

The PL/SQL uses the ordering to compute the Boolean expressions like x > y, and to do comparisons implied by the GROUP BY, DISTINCT, and ORDER BY clauses. The Map method convert returns to the relative position of an object in the ordering of all the rational objects.

An object type can have only one map method that should be a parameter less function with one of the scalar return types shown below: DATE, VARCHAR2, NUMBER, or an ANSI SQL type like CHARACTER or REAL.

On the other hand, you can supply the PL/SQL with an order method. An object type can have only one order method that should be a function which returns a numeric result. In the illustration below, the keyword ORDER indicates that method match compares 2 objects:

CREATE TYPE Customer AS OBJECT (

id NUMBER,

name VARCHAR2(20),

addr VARCHAR2(30),

ORDER MEMBER FUNCTION match (c Customer) RETURN INTEGER

);

CREATE TYPE BODY Customer AS

ORDER MEMBER FUNCTION match (c Customer) RETURN INTEGER IS

BEGIN

IF id < c.id THEN

RETURN -1; -- any negative number will do

ELSIF id > c.id THEN

RETURN 1; -- any positive number will do

ELSE

RETURN 0;

END IF;

END;

END;

Every order method takes merely two parameters: the built-in parameter SELF & the other object of similar type. If c1 and c2 are Customer objects, a comparison like c1 > c2 calls method match automatically. The method returns a , zero, negative number or a positive number suggesting that the SELF is correspondingly less than, equal to, or greater than the other parameter. If whichever parameter passed to an order method is null, then the method returns a null.

Posted Date: 10/6/2012 8:09:45 AM | Location : United States







Related Discussions:- Map and order methods, Assignment Help, Ask Question on Map and order methods, Get Answer, Expert's Help, Map and order methods Discussions

Write discussion on Map and order methods
Your posts are moderated
Related Questions
IN Mode An IN parameter pass the values to the subprogram being called. Within the subprogram, an IN parameter acts like a constant. And hence, it cannot be assigned a value.

Using ROLLBACK The ROLLBACK statements end the present transaction and undo any change made during the transaction. The Rolling back is helpful for two reasons. Firstly, if yo

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

Table Literals - SQL One might expect SQL to support table literals in the manner illustrated in Example 2.2, but in fact that is not a legal SQL expression. Example: Not a

Transactions in SQL BEGIN TRANSACTION, COMMIT, and ROLLBACK, SQL has the same syntax except for START in place of BEGIN. However, START TRANSACTION is used only for outermost

Parameter Modes: You do not require to specify a parameter mode for the input bind arguments (those used, for illustration, in the WHERE clause) as the mode defaults to IN. Th

Some Varray Examples In SQL Plus, assume that you define an object type Project, as described below: SQL> CREATE TYPE Project AS OBJECT ( 2 project_no NUMBER(2), 3 title VARCHA

Lightweight system to provide and take info from workers in the field and office, have basic design outlined already just require build and implementation Desired Skills CSS,

WHEN or THEN Key Constraints Suppose a table has two columns representing a period of time throughout which the information conveyed by the other columns is recorded as having

LIKE Operator You use the LIKE operator to compare the character value to a pattern. The Case is significant. LIKE returns the Boolean value TRUE when the character patterns mat