PL/SQL - EXCEPTIONS
PL/SQL - EXCEPTIONS:-
In this chapter, we will discuss Exceptions in PL/SQL. An exception is an error condition during a program execution. PL/SQL supports programmers to catch
such conditions using EXCEPTION block in the program and an appropriate action is taken against the error condition. There are two types of exceptions −
System-defined exceptions
User-defined exceptions
Syntax for Exception Handling
The general syntax for exception handling is as follows. Here you can list down as many exceptions as you can handle. The default exception will be handled
using WHEN others THEN −
DECLARE
<declarations section>
BEGIN
<executable command(s)>
EXCEPTION
<exception handling goes here >
WHEN exception1 THEN
exception1-handling-statements
WHEN exception2 THEN
exception2-handling-statements
WHEN exception3 THEN
exception3-handling-statements
........
WHEN others THEN
exception3-handling-statements
END;
Example
Let us write a code to illustrate the concept. We will be using the CUSTOMERS table we had created and used in the previous chapters −
DECLARE
c_id customers.id%type := 8;
c_name customerS.No.ame%type;
c_addr customers.address%type;
BEGIN
SELECT name, address INTO c_name, c_addr
FROM customers
WHERE id = c_id;
DBMS_OUTPUT.PUT_LINE ('Name: '|| c_name);
DBMS_OUTPUT.PUT_LINE ('Address: ' || c_addr);
EXCEPTION
WHEN no_data_found THEN
dbms_output.put_line('No such customer!');
WHEN others THEN
dbms_output.put_line('Error!');
END;
/
When the above code is executed at the SQL prompt, it produces the following result −
No such customer!
PL/SQL procedure successfully completed.
The above program displays the name and address of a customer whose ID is given. Since there is no customer with ID value 8 in our database, the program
raises the run-time exception NO_DATA_FOUND, which is captured in the EXCEPTION block.
Raising Exceptions
Exceptions are raised by the database server automatically whenever there is any internal database error, but exceptions can be raised explicitly by the
programmer by using the command RAISE. Following is the simple syntax for raising an exception −
DECLARE
exception_name EXCEPTION;
BEGIN
IF condition THEN
RAISE exception_name;
END IF;
EXCEPTION
WHEN exception_name THEN
statement;
END;
You can use the above syntax in raising the Oracle standard exception or any user-defined exception. In the next section, we will give you an example on
raising a user-defined exception. You can raise the Oracle standard exceptions in a similar way.
User-defined Exceptions
PL/SQL allows you to define your own exceptions according to the need of your program. A user-defined exception must be declared and then raised explicitly,
using either a RAISE statement or the procedure DBMS_STANDARD.RAISE_APPLICATION_ERROR.
The syntax for declaring an exception is −
DECLARE
my-exception EXCEPTION;
Example
The following example illustrates the concept. This program asks for a customer ID, when the user enters an invalid ID, the exception invalid_id is raised.
DECLARE
c_id customers.id%type := &cc_id;
c_name customerS.No.ame%type;
c_addr customers.address%type;
-- user defined exception
ex_invalid_id EXCEPTION;
BEGIN
IF c_id <= 0 THEN
RAISE ex_invalid_id;
ELSE
SELECT name, address INTO c_name, c_addr
FROM customers
WHERE id = c_id;
DBMS_OUTPUT.PUT_LINE ('Name: '|| c_name);
DBMS_OUTPUT.PUT_LINE ('Address: ' || c_addr);
END IF;
EXCEPTION
WHEN ex_invalid_id THEN
dbms_output.put_line('ID must be greater than zero!');
WHEN no_data_found THEN
dbms_output.put_line('No such customer!');
WHEN others THEN
dbms_output.put_line('Error!');
END;
/
When the above code is executed at the SQL prompt, it produces the following result −
Enter value for cc_id: -6 (let's enter a value -6)
old 2: c_id customers.id%type := &cc_id;
new 2: c_id customers.id%type := -6;
ID must be greater than zero!
PL/SQL procedure successfully completed.
Pre-defined Exceptions
PL/SQL provides many pre-defined exceptions, which are executed when any database rule is violated by a program. For example, the predefined exception
NO_DATA_FOUND is raised when a SELECT INTO statement returns no rows. The following table lists few of the important pre-defined exceptions −
Exception
Oracle
Error
SQLCODE Description
ACCESS_INTO_NULL 06530 -6530 It is raised when a null object is automatically assigned a value.
CASE_NOT_FOUND 06592 -6592
It is raised when none of the choices in the WHEN clause of a CASE statement is selected, and there
is no ELSE clause.
COLLECTION_IS_NULL 06531 -6531
It is raised when a program attempts to apply collection methods other than EXISTS to an
uninitialized nested table or varray, or the program attempts to assign values to the elements of an
uninitialized nested table or varray.
DUP_VAL_ON_INDEX 00001 -1 It is raised when duplicate values are attempted to be stored in a column with unique index.
INVALID_CURSOR 01001 -1001
It is raised when attempts are made to make a cursor operation that is not allowed, such as closing an
unopened cursor.
INVALID_NUMBER 01722 -1722
It is raised when the conversion of a character string into a number fails because the string does not
represent a valid number.
LOGIN_DENIED 01017 -1017 It is raised when a program attempts to log on to the database with an invalid username or password.
NO_DATA_FOUND 01403 +100 It is raised when a SELECT INTO statement returns no rows.
NOT_LOGGED_ON 01012 -1012 It is raised when a database call is issued without being connected to the database.
PROGRAM_ERROR 06501 -6501 It is raised when PL/SQL has an internal problem.
ROWTYPE_MISMATCH 06504 -6504 It is raised when a cursor fetches value in a variable having incompatible data type.
SELF_IS_NULL 30625 -30625 It is raised when a member method is invoked, but the instance of the object type was not initialized.
STORAGE_ERROR 06500 -6500 It is raised when PL/SQL ran out of memory or memory was corrupted.
TOO_MANY_ROWS 01422 -1422 It is raised when a SELECT INTO statement returns more than one row.
VALUE_ERROR 06502 -6502 It is raised when an arithmetic, conversion, truncation, or sizeconstraint error occurs.
ZERO_DIVIDE 01476 1476 It is raised when an attempt is made to divide a number by zero.
In this chapter, we will discuss Exceptions in PL/SQL. An exception is an error condition during a program execution. PL/SQL supports programmers to catch
such conditions using EXCEPTION block in the program and an appropriate action is taken against the error condition. There are two types of exceptions −
System-defined exceptions
User-defined exceptions
Syntax for Exception Handling
The general syntax for exception handling is as follows. Here you can list down as many exceptions as you can handle. The default exception will be handled
using WHEN others THEN −
DECLARE
<declarations section>
BEGIN
<executable command(s)>
EXCEPTION
<exception handling goes here >
WHEN exception1 THEN
exception1-handling-statements
WHEN exception2 THEN
exception2-handling-statements
WHEN exception3 THEN
exception3-handling-statements
........
WHEN others THEN
exception3-handling-statements
END;
Example
Let us write a code to illustrate the concept. We will be using the CUSTOMERS table we had created and used in the previous chapters −
DECLARE
c_id customers.id%type := 8;
c_name customerS.No.ame%type;
c_addr customers.address%type;
BEGIN
SELECT name, address INTO c_name, c_addr
FROM customers
WHERE id = c_id;
DBMS_OUTPUT.PUT_LINE ('Name: '|| c_name);
DBMS_OUTPUT.PUT_LINE ('Address: ' || c_addr);
EXCEPTION
WHEN no_data_found THEN
dbms_output.put_line('No such customer!');
WHEN others THEN
dbms_output.put_line('Error!');
END;
/
When the above code is executed at the SQL prompt, it produces the following result −
No such customer!
PL/SQL procedure successfully completed.
The above program displays the name and address of a customer whose ID is given. Since there is no customer with ID value 8 in our database, the program
raises the run-time exception NO_DATA_FOUND, which is captured in the EXCEPTION block.
Raising Exceptions
Exceptions are raised by the database server automatically whenever there is any internal database error, but exceptions can be raised explicitly by the
programmer by using the command RAISE. Following is the simple syntax for raising an exception −
DECLARE
exception_name EXCEPTION;
BEGIN
IF condition THEN
RAISE exception_name;
END IF;
EXCEPTION
WHEN exception_name THEN
statement;
END;
You can use the above syntax in raising the Oracle standard exception or any user-defined exception. In the next section, we will give you an example on
raising a user-defined exception. You can raise the Oracle standard exceptions in a similar way.
User-defined Exceptions
PL/SQL allows you to define your own exceptions according to the need of your program. A user-defined exception must be declared and then raised explicitly,
using either a RAISE statement or the procedure DBMS_STANDARD.RAISE_APPLICATION_ERROR.
The syntax for declaring an exception is −
DECLARE
my-exception EXCEPTION;
Example
The following example illustrates the concept. This program asks for a customer ID, when the user enters an invalid ID, the exception invalid_id is raised.
DECLARE
c_id customers.id%type := &cc_id;
c_name customerS.No.ame%type;
c_addr customers.address%type;
-- user defined exception
ex_invalid_id EXCEPTION;
BEGIN
IF c_id <= 0 THEN
RAISE ex_invalid_id;
ELSE
SELECT name, address INTO c_name, c_addr
FROM customers
WHERE id = c_id;
DBMS_OUTPUT.PUT_LINE ('Name: '|| c_name);
DBMS_OUTPUT.PUT_LINE ('Address: ' || c_addr);
END IF;
EXCEPTION
WHEN ex_invalid_id THEN
dbms_output.put_line('ID must be greater than zero!');
WHEN no_data_found THEN
dbms_output.put_line('No such customer!');
WHEN others THEN
dbms_output.put_line('Error!');
END;
/
When the above code is executed at the SQL prompt, it produces the following result −
Enter value for cc_id: -6 (let's enter a value -6)
old 2: c_id customers.id%type := &cc_id;
new 2: c_id customers.id%type := -6;
ID must be greater than zero!
PL/SQL procedure successfully completed.
Pre-defined Exceptions
PL/SQL provides many pre-defined exceptions, which are executed when any database rule is violated by a program. For example, the predefined exception
NO_DATA_FOUND is raised when a SELECT INTO statement returns no rows. The following table lists few of the important pre-defined exceptions −
Exception
Oracle
Error
SQLCODE Description
ACCESS_INTO_NULL 06530 -6530 It is raised when a null object is automatically assigned a value.
CASE_NOT_FOUND 06592 -6592
It is raised when none of the choices in the WHEN clause of a CASE statement is selected, and there
is no ELSE clause.
COLLECTION_IS_NULL 06531 -6531
It is raised when a program attempts to apply collection methods other than EXISTS to an
uninitialized nested table or varray, or the program attempts to assign values to the elements of an
uninitialized nested table or varray.
DUP_VAL_ON_INDEX 00001 -1 It is raised when duplicate values are attempted to be stored in a column with unique index.
INVALID_CURSOR 01001 -1001
It is raised when attempts are made to make a cursor operation that is not allowed, such as closing an
unopened cursor.
INVALID_NUMBER 01722 -1722
It is raised when the conversion of a character string into a number fails because the string does not
represent a valid number.
LOGIN_DENIED 01017 -1017 It is raised when a program attempts to log on to the database with an invalid username or password.
NO_DATA_FOUND 01403 +100 It is raised when a SELECT INTO statement returns no rows.
NOT_LOGGED_ON 01012 -1012 It is raised when a database call is issued without being connected to the database.
PROGRAM_ERROR 06501 -6501 It is raised when PL/SQL has an internal problem.
ROWTYPE_MISMATCH 06504 -6504 It is raised when a cursor fetches value in a variable having incompatible data type.
SELF_IS_NULL 30625 -30625 It is raised when a member method is invoked, but the instance of the object type was not initialized.
STORAGE_ERROR 06500 -6500 It is raised when PL/SQL ran out of memory or memory was corrupted.
TOO_MANY_ROWS 01422 -1422 It is raised when a SELECT INTO statement returns more than one row.
VALUE_ERROR 06502 -6502 It is raised when an arithmetic, conversion, truncation, or sizeconstraint error occurs.
ZERO_DIVIDE 01476 1476 It is raised when an attempt is made to divide a number by zero.
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