Exception Handling in Pl/Sql

PL/SQL provides the mechanism to handle any unexpected error/exception using reserved keyword ‘EXCEPTION’.

PL/SQL Exception message consists of three parts.

i)                    Type of Exception

ii)                   An Error Code

iii)                 A message

Syntax:-

DECLARE

   Declaration part

 BEGIN

   Execution part

 EXCEPTION

 WHEN ex_name1 THEN

    Statement

 WHEN ex_name2 THEN

    Statement

 WHEN Others THEN

   Statement

END;

Types of Exception:-

Named System Exceptions:

DUP_VAL_ON_INDEX	ORA-00001	You tried to execute an INSERT or UPDATE statement that has created a duplicate value in a field restricted by a unique index.
TIMEOUT_ON_RESOURCE	ORA-00051	You were waiting for a resource and you timed out.
TRANSACTION_BACKED_OUT	ORA-00061	The remote portion of a transaction has rolled back.
INVALID_CURSOR	ORA-01001	You tried to reference a cursor that does not yet exist. This may have happened because you've executed a FETCH cursor or CLOSE cursor before OPENing the cursor.
NOT_LOGGED_ON	ORA-01012	You tried to execute a call to Oracle before logging in.
LOGIN_DENIED	ORA-01017	You tried to log into Oracle with an invalid username/password combination.
NO_DATA_FOUND	ORA-01403	You tried one of the following: 1.     You executed a SELECT INTO statement and no rows were returned. 2.     You referenced an uninitialized row in a table. 3.     You read past the end of file with the UTL_FILE package.
TOO_MANY_ROWS	ORA-01422	You tried to execute a SELECT INTO statement and more than one row was returned.
ZERO_DIVIDE	ORA-01476	You tried to divide a number by zero.
INVALID_NUMBER	ORA-01722	You tried to execute a SQL statement that tried to convert a string to a number, but it was unsuccessful.
STORAGE_ERROR	ORA-06500	You ran out of memory or memory was corrupted.
PROGRAM_ERROR	ORA-06501	This is a generic "Contact Oracle support" message because an internal problem was encountered.
VALUE_ERROR	ORA-06502	You tried to perform an operation and there was a error on a conversion, truncation, or invalid constraining of numeric or character data.
CURSOR_ALREADY_OPEN	ORA-06511	You tried to open a cursor that is already open.

Named Programmer defined exceptions:-

It is necessary for programmers to define their own exceptions, which aren't defined by PL/SQL. These are called Named Programmer-Defined Exceptions.

When Others Clause:-

                This is to handle all other exceptions which are neither getting handled by ‘Named System Exceptions’ and nor by ‘Named Programmer defined exceptions’.

Syntax:

…..

                EXCEPTION

                                When excep_1 Then

                                                [Statement]

When excep_2 Then

                                                [Statement]

When Others Then

                                                raise_application_error(-20001,'An error was encountered’);

END;

What is RAISE_APPLICATION_ERROR ( ):-

                It is a built-in procedure in oracle which is used to display the user-defined error messages along with the error number.