Oracle/PLSQL: Named Programmer-Defined Exceptions

What is a named programmer-defined exception?

Sometimes, it is necessary for programmers to name and trap their own exceptions - ones that aren't defined already by PL/SQL. These are called Named Programmer-Defined Exceptions.

The syntax for the Named Programmer-Defined Exception in a procedure is:

CREATE [OR REPLACE] PROCEDURE procedure_name     [ (parameter [,parameter]) ] IS     [declaration_section]

    exception_name EXCEPTION;

BEGIN     executable_section

    RAISE exception_name ;

EXCEPTION     WHEN exception_name THEN         [statements]

    WHEN OTHERS THEN         [statements]

END [procedure_name];

The syntax for the Named Programmer-Defined Exception in a function is:

CREATE [OR REPLACE] FUNCTION function_name     [ (parameter [,parameter]) ]     RETURN return_datatype IS | AS     [declaration_section]

    exception_name EXCEPTION;

BEGIN     executable_section

    RAISE exception_name ;

EXCEPTION     WHEN exception_name THEN         [statements]

    WHEN OTHERS THEN         [statements]

END [function_name];

Here is an example of a procedure that uses a Named Programmer-Defined Exception:

CREATE OR REPLACE PROCEDURE add_new_order     (order_id_in IN NUMBER, sales_in IN NUMBER) IS     no_sales EXCEPTION;

BEGIN     IF sales_in = 0 THEN         RAISE no_sales;

ELSE     INSERT INTO orders (order_id, total_sales )     VALUES ( order_id_in, sales_in ); END IF;

EXCEPTION      WHEN no_sales THEN         raise_application_error (-20001,'You must have sales in order to submit the order.');

    WHEN OTHERS THEN         raise_application_error (-20002,'An error has occurred inserting an order.');

END;

In this example, we have declared a Named Programmer-Defined Exception called no_sales in our declaration statement with the following code:

no_sales EXCEPTION;

We've then raised the exception in the executable section of the code:

 IF sales_in = 0 THEN         RAISE no_sales;

Now if the sales_in variable contains a zero, our code will jump directly to the Named Programmer-Defined Exception called no_sales.

Finally, we tell our procedure what to do when the no_sales exception is encountered by including code in the WHEN clause:

WHEN no_sales THEN         raise_application_error (-20001,'You must have sales in order to submit the order.');

We are also using the WHEN OTHERS clause to trap all remaining exceptions:

 WHEN OTHERS THEN         raise_application_error (-20002,'An error has occurred inserting an order.');