Avoiding collection exceptions, PL-SQL Programming

Avoiding Collection Exceptions 

In many cases, if you reference a nonexistent collection element, then PL/SQL raises a predefined exception. Consider the illustration shown below:

DECLARE

TYPE NumList IS TABLE OF NUMBER;

nums NumList; -- atomically null

BEGIN

/* Assume execution continues despite the raised exceptions. */

nums(1) := 1; -- raises COLLECTION_IS_NULL (1)

nums := NumList(1,2); -- initialize table

nums(NULL) := 3 -- raises VALUE_ERROR (2)

nums(0) := 3; -- raises SUBSCRIPT_OUTSIDE_LIMIT (3)

nums(3) := 3; -- raises SUBSCRIPT_BEYOND_COUNT (4)

nums.DELETE(1); -- delete element 1

IF nums(1) = 1 THEN ... -- raises NO_DATA_FOUND (5)

In the first situation, the nested table is automatically null. In the second situation, the subscript is null. In the third situation, the subscript is outside the legal range. In the fourth situation, the subscripts exceed the number of elements in the table. In the fifth situation, the subscript designates a deleted element.

The list below shows when a given exception is raised:

2127_collection exception.png

In many cases, you can pass "invalid" subscripts to a method without raising the exception. For illustration, if you pass a null subscript to the procedure DELETE, it does nothing. You can also replace the deleted elements without raising NO_DATA_FOUND, as the example below shows:

DECLARE

TYPE NumList IS TABLE OF NUMBER;

nums NumList := NumList(10,20,30); -- initialize table

BEGIN

...

nums.DELETE(-1); -- does not raise SUBSCRIPT_OUTSIDE_LIMIT

nums.DELETE(3); -- delete 3rd element

DBMS_OUTPUT.PUT_LINE(nums.COUNT); -- prints 2

nums(3) := 30; -- legal; does not raise NO_DATA_FOUND

DBMS_OUTPUT.PUT_LINE(nums.COUNT); -- prints 3

END;

The Packaged collection types and the local collection types are never compatible. For example, assume that you want to call the following packaged process:

CREATE PACKAGE pkg1 AS

TYPE NumList IS VARRAY(25) OF NUMBER(4);

PROCEDURE delete_emps (emp_list NumList);

...

END pkg1;

CREATE PACKAGE BODY pkg1 AS

PROCEDURE delete_emps (emp_list NumList) IS ...

...

END pkg1;

If you run the PL/SQL block below, then the second procedure call fails with a wrong number or types of arguments error. This is because the packaged and local VARRAY types are incompatible even though their definitions are same.

DECLARE

TYPE NumList IS VARRAY(25) OF NUMBER(4);

emps pkg1.NumList := pkg1.NumList(7369, 7499);

emps2 NumList := NumList(7521, 7566);

BEGIN

pkg1.delete_emps(emps);

pkg1.delete_emps(emps2); -- causes a compilation error

END;

Posted Date: 10/4/2012 3:23:59 AM | Location : United States







Related Discussions:- Avoiding collection exceptions, Assignment Help, Ask Question on Avoiding collection exceptions, Get Answer, Expert's Help, Avoiding collection exceptions Discussions

Write discussion on Avoiding collection exceptions
Your posts are moderated
Related Questions
Table Comparison - SQL The following definitions for relation comparisons: Let r1 and r2 be relations having the same heading. Then: r1 ⊆ r2 is true if every tuple of r1

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

Named Notation The second procedure call uses the named notation. An arrow (=>) serve as the relationship operator that associates the formal parameter to the left of the arro

1- You can check attribute names from each table in DBF11 by running for example:  desc dbf11.Member;  desc dbf11.Agent;  desc dbf11.Producer; Because some attribute names in

MECHANISTI S THEORY-HAECKEL (1866) - Haeckel stating that after each catalysm, some new organism suddenly forms as a chance event in one stride from inanimate matter and sub

Relational Operators The relational operators permit you to compare randomly complex expressions. The list below provides the meaning of each operator:

1. Create a procedure called TAX_COST_SP to accomplish the tax calculation task. Keep in mind that the state and subtotal values are inputs into the procedure and the procedure is

Initializing Records The illustration below shows that you can initialize a record in its type definition. Whenever you declare a record of the type TimeRec, its 3 fields supp

Block Structure The PL/SQL is a block-structured language. That is, the fundamental units (procedures, anonymous blocks, and functions) that make up a PL/SQL program are logi

Truth Tables: However in propositional logic - here we are restricted to expressing sentences and where the propositions are true or false - so we can check where a particular