Exception handling, PL-SQL Programming

Exception handling

In the PL/SQL, a warning or error condition is known as an exception. The Exceptions can be internally defined (by the run-time system) or user defined. The Examples of internally defined exceptions involve division by zero and out of memory. Some familiar internal exceptions have predefined names, like ZERO_DIVIDE and STORAGE_ERROR.

You can define exceptions of your own in the declarative part of any PL/SQL subprogram, block, or package. For illustration, you might define an exception namely the insufficient_funds to flag overdrawn bank accounts. Dissimilar internal exceptions, user-defined exceptions should be given names.

Whenever errors occur, an exception is raised. That is, the normal execution stops and control transfers to the exception-handling section of your PL/SQL subprogram or block. The Internal exceptions are raised implicitly (automatically) by the run-time system. The User-defined exceptions should be raised explicitly by the RAISE statements that can also raise the predefined exceptions.

To handle the raised exceptions, you write individual routines known as the exception handlers.

Later an exception handler runs, the present block stops executing and the enclosing block resumes with the next statement. If there is no enclosing block, the control returns to the host atmosphere.

In the illustration below, you compute and store a price-to-earnings ratio for a company with ticker symbol XYZ. The predefined exception ZERO_DIVIDE is raised whenever the company has zero earnings. This stops general execution of the block and transfers control to the exception handlers. The elective OTHERS handler catches all the exceptions which the block does not name explicitly.

DECLARE

pe_ratio NUMBER(3,1);

BEGIN

SELECT price / earnings INTO pe_ratio FROM stocks

WHERE symbol = 'XYZ'; -- might cause division-by-zero error

INSERT INTO stats (symbol, ratio) VALUES ('XYZ', pe_ratio);

COMMIT;

EXCEPTION -- exception handlers begin

WHEN ZERO_DIVIDE THEN -- handles 'division by zero' error

INSERT INTO stats (symbol, ratio) VALUES ('XYZ', NULL);

COMMIT;

...

WHEN OTHERS THEN -- handles all other errors

ROLLBACK;

END; -- exception handlers and block end here

The last illustration describes an exception handling, which is not the effective use of INSERT statements. For illustration, an enhanced way to do the insert is as shown:

INSERT INTO stats (symbol, ratio)

SELECT symbol, DECODE(earnings, 0, NULL, price / earnings)

FROM stocks WHERE symbol = 'XYZ';

Posted Date: 10/5/2012 5:04:12 AM | Location : United States







Related Discussions:- Exception handling, Assignment Help, Ask Question on Exception handling, Get Answer, Expert's Help, Exception handling Discussions

Write discussion on Exception handling
Your posts are moderated
Related Questions
Important Distinctions The list of important distinctions are given below: Value versus variable Syntax versus semantics Variable versus variable reference

Negation (NOT, ¬) - SQL There are three rows instead of just two. As you can see, ¬ p is defined as in two-valued logic (2VL) when p is either true or false, but ¬ (unknown) i

Fetching from a Cursor Variable The FETCH statement retrieve rows one at a time from the product set of a multi-row query. The syntax for the same is as shown: FETCH {curso

DBMS_OUTPUT: The Package DBMS_OUTPUT enables you to display output from the PL/SQL subprograms and blocks, that makes it easier to test and debug them. The procedure put_ line

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

Using Aggregation on Nested Tables Example is the most direct translation of its counterpart in the theory book that can be obtained in SQL but it is so over-elaborate that no

Why Use Cursor Variables ? Primarily, you use the cursor variables to pass the query result sets between the PL/SQL stored subprograms and different clients. Neither PL/SQL nor

How Transactions Guard Your Database The transaction is a sequence of SQL data manipulation statements which does a logical unit of work. The Oracle treats the sequence of SQL

UPDATE Statement   The UPDATE statement transforms the values of the specified columns in one or more rows in the table or view. Syntax:

Manipulating Collections Within PL/SQL, the collections add procedural power and flexibility. The biggest benefit is that your program can compute subscripts to process the spec