Assigning and comparing collections, PL-SQL Programming

Assignment Help:

Assigning and Comparing Collections

One collection can be assigned to other by an SELECT, INSERT, UPDATE, or FETCH statement, an assignment statement, or by a subprogram call. As the illustration shown below, the collections should have the same datatype. Having the similar element type is not enough.

DECLARE
TYPE Clientele IS VARRAY(100) OF Customer;
TYPE Vips IS VARRAY(100) OF Customer;
group1 Clientele := Clientele(...);
group2 Clientele := Clientele(...);
group3 Vips := Vips(...);
BEGIN
group2 := group1;
group3 := group2; -- illegal;


Various datatypes becomes automatically null (and should be reinitialized). Now consider the illustration as shown below:

 
DECLARE
TYPE Clientele IS TABLE OF Customer;
group1 Clientele := Clientele(...); -- initialized
group2 Clientele; -- atomically null
BEGIN
IF group1 IS NULL THEN ... -- condition yields FALSE
group1 := group2;
IF group1 IS NULL THEN ... -- condition yields TRUE
...
END;


Similarly, if you assign the non-value NULL to a collection, the collection becomes automatically null.


Assigning Collection Elements

You can assign the value of an expression to the specific element in a collection by using the syntax

collection_name(subscript) := expression;



Where the expression yields a value of the type specified for elements in the collection type definition. If the subscript is null or not convertible to an integer, the PL/SQL raises the predefined exception VALUE_ERROR. If the collection is automatically null, then the PL/SQL raises COLLECTION_IS_NULL. Some of the examples are shown below:




DECLARE
TYPE NumList IS TABLE OF INTEGER;
nums NumList := NumList(10,20,30);
ints NumList;
...
BEGIN
...
nums(1) := TRUNC(high/low);
nums(3) := nums(1);
nums(2) := ASCII(’B’);
/* Assume execution continues despite the raised exception. */
nums(’A’) := 40; -- raises VALUE_ERROR
ints(1) := 15; -- raises COLLECTION_IS_NULL
END;


Comparing Whole Collections

The Nested tables and varrays can be automatically null; therefore they can be tested for the nullity, as the example below shows:

DECLARE
TYPE Staff IS TABLE OF Employee;
members Staff;
BEGIN
...
IF members IS NULL THEN ... -- condition yields TRUE;
END;


Though, the collections cannot be compared for equality or inequality. For illustration, the IF condition below is illegal as shown:

DECLARE
TYPE Clientele IS TABLE OF Customer;
group1 Clientele := Clientele(...);
group2 Clientele := Clientele(...);
BEGIN
...
IF group1 = group2 THEN -- causes compilation error
...
END IF;
END;
This restriction also applies to implicit the comparisons. For illustration, the collections cannot appear in an ORDER BY, GROUP BY, or DISTINCT list.


Related Discussions:- Assigning and comparing collections

Difference between ttitle and btitle, TTITLE and BTITLE are commands in Pl-...

TTITLE and BTITLE are commands in Pl-SQL to control report headings and footers. This Ttitle & Btitle are mainly used on creating SQL*PLUS report. Ttitle is used for toptitle headi

Cartesian product, Using a Join on 2 tables, select all columns and all row...

Using a Join on 2 tables, select all columns and all rows from the tables without the use of a Cartesian product. Query: SELECT * FROM EMPLOYEE1 JOIN CONTRACT ON EMPLOYEE

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

Ssrs report writing, SSRS Report Writing Project Description: This re...

SSRS Report Writing Project Description: This report is part of a larger project to make a SQL Server Reporting Service (SSRS) based reporting solution. There can be more rep

Data types in sql - character, Data Types in SQL - Character CHARACTER...

Data Types in SQL - Character CHARACTER or, synonymously, CHAR, for character strings. When this type is to be the declared type of something (e.g., a column), the permissible

Keys in sql, Keys in SQL SQL support for keys in the following respect...

Keys in SQL SQL support for keys in the following respects: SQL does not require at least one key for every base table. If no key is explicitly declared, then KEY {ALL B

Using delete - collection method, Using DELETE This process has three ...

Using DELETE This process has three forms. The DELETE removes all elements from the collection. DELETE(n) removes the nth element from the nested table. When n is null, then D

Pass the nulls to a dynamic sql, Pass the nulls to a dynamic SQL: Pas...

Pass the nulls to a dynamic SQL: Passing Nulls: Assume that you want to pass the nulls to a dynamic SQL statement. For illustration, you may write the EXECUTE IMMEDIATE

Introduction to oracle, Introduction Oracle 9i - it was made publ...

Introduction Oracle 9i - it was made public in the year 2001 with over 400 features, and graphics, it has merged the traditional business with modern internet application

Write an anonymous block that contains a pl/sql function, a. Write an anon...

a. Write an anonymous block that contains a PL/SQL function. Given an order number orderNo, the function will calculate the total number of the parts in the order. Then the anonym

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