Avoiding collection exceptions, PL-SQL Programming

Assignment Help:

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;


Related Discussions:- Avoiding collection exceptions

Initializing and referencing collections, Initializing and Referencing Coll...

Initializing and Referencing Collections Until you initialize a collection, a nested table or varray is automatically null (i.e. the collection itself is null, not its elements)

Example of delete - sql, Example of DELETE - SQL As with UPDATE, a FOR...

Example of DELETE - SQL As with UPDATE, a FOR PORTION OF clause can be specified if the target table has a defined period name, as illustrated in Example. Example: Deleting

Union all - sql, UNION ALL - SQL Further varieties of UNION arise when...

UNION ALL - SQL Further varieties of UNION arise when we replace the key word DISTINCT by ALL in any of the foregoing examples, as in Example. ALL specifies that if row r appe

Parameter and keyword description - packages, Parameter and Keyword Descrip...

Parameter and Keyword Description: package_name: This construct identifies the package. AUTHID Clause: This determine whether all the packaged subprograms impleme

Nested tables versus index-by tables, Nested Tables versus Index-by Tables ...

Nested Tables versus Index-by Tables The Index-by tables and nested tables are just similar. For e.g.  They have similar structure and their individual elements are accessed in

Authorisations - privileges, Authorisations - Privileges As relational...

Authorisations - Privileges As relational theory is silent on the issue of authorisation, it offers nothing with which SQL's vast edifice in support of what it calls privilege

Implicit rollbacks, Implicit Rollbacks Before execute the INSERT, UPDA...

Implicit Rollbacks Before execute the INSERT, UPDATE, or DELETE statement, the Oracle marks an implicit savepoint . When the statement fails, the Oracle rolls back to the save

Example of not exists operator - sql, Example of NOT EXISTS Operator - SQL ...

Example of NOT EXISTS Operator - SQL Example is a translation into SQL of the corresponding example, which is included there merely to show that for any scalar comparison the

Mysql developer/programmer, Project Description: I want somebody who can...

Project Description: I want somebody who can help me with an idea that I have been working on for a few months now. The person will require extensive knowledge of warcraft 3 PvP

Null statement-sequential control, NULL Statement The NULL statement c...

NULL Statement The NULL statement clearly specifies in action; it does nothing other than to pass control to the next statement. It can, though, improve the readability. In a

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