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
Naming Conventions The similar naming conventions apply to all PL/SQL program items and units including the variables, cursors, constants, cursor variables, procedures, exception

Using Invoker Rights: By default, the stored procedure executes with the privileges of its definer, not its invoker. These procedures are bound to the schema in which they inh

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

Literature review

WHILE-LOOP The WHILE-LOOP statement relates a condition with the series of statements enclosed by the keywords LOOP and END LOOP, as shown: WHILE condition LOOP sequence_of_sta

Cause of Indeterminacy in SQL One root cause of indeterminacy in SQL lies in its implementation of comparison for equality. For certain system-defined types it is possible for

Example of Table Literal - SQL Example: A Table Literal (correct version) VALUES ('S1', 'C1', 'Anne'), ('S1', 'C2', 'Anne'), ('S2', 'C1', 'Boris'), ('S3', 'C3'

OPEN-FOR Statement The OPEN-FOR statements execute the multi-row query related with a cursor variable. It also allocates the resources used by the Oracle to process the query a

Write a stored procedure that accepts the post code in which the customer resides as the input parameter. The procedure should then use an explicit cursor to display comprehensive

Parameter and Keyword Description: cursor_variable_name: This identifies a cursor variable or the parameter formerly declared within the present scope. host_cursor_va