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

How exceptions propagate in pl/sql programming?, How Exceptions Propagate ?...

How Exceptions Propagate ? Whenever an exception is raised, and if the PL/SQL cannot find a handler for it in the present subprogram or block, the exception propagates. That is

Triggers, At times, customers make mistakes in submitting their orders and ...

At times, customers make mistakes in submitting their orders and call to cancel the order. Brewbean’s wants to create a trigger that automatically updates the stock level of all pr

Primary key - sql, Primary Key - SQL A PRIMARY KEY specification carri...

Primary Key - SQL A PRIMARY KEY specification carries an implicit NOT NULL constraint on each column of the specified key. When more than one key constraint is required, the k

Implicit cursor attributes, Implicit Cursor Attributes The Implicit cur...

Implicit Cursor Attributes The Implicit cursor attributes returns the information about the execution of an INSERT, DELETE, UPDATE, or SELECT INTO statement. The cursor attribu

Features of pl/sql, Main features of PL/SQL A good way to get familiar ...

Main features of PL/SQL A good way to get familiar with PL/SQL is to look at a sample program. The below program processes an order for tennis rackets. At first, it declares a

Delimiters, Delimiters A delimiter is a simple or compound symbol whi...

Delimiters A delimiter is a simple or compound symbol which has a special meaning to PL/SQL. For example, you use delimiters to symbolize an arithmetic operation like additio

program for employees -ado.net framework , Challenge 1 You are require...

Challenge 1 You are required to do the project and write a test plan for it. Demo 4 is a check writer program for employees. In it, the user enters all information about the

Keyword and parameter description - cursors, Keyword and Parameter Descript...

Keyword and Parameter Description select_statement: This is a query which returns a result set of the rows. Its syntax is such that of select_ into_statement without the IN

Example of group by and collect operator, Example of GROUP BY and COLLECT O...

Example of GROUP BY and COLLECT Operator Example: Using GROUP BY and COLLECT to obtain C_ER2 SELECT CourseId, CAST ( COLLECT (ROW (StudentId, Mark)) AS ROW (Studen

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

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