PRAGMA EXCEPTION_INIT associates a user-defined error code with an exception. A PRAGMA EXCEPTION_INIT declaration may be included in any block, sub-block, or package. You can only assign an error code to an exception (using PRAGMA EXCEPTION_INIT) after declaring the exception. The format of a PRAGMA EXCEPTION_INIT declaration is as follows:

PRAGMA EXCEPTION_INIT(exception_name,
                      {exception_number | exception_code})

where:

  • exception_name is the name of the associated exception.
  • exception_number is a user-defined error code associated with the pragma. If you specify an unmapped exception_number value, the server will return a warning.
  • exception_code is the name of a predefined exception. For a complete list of valid exceptions, see the PostgreSQL core documentation available at: https://www.postgresql.org/docs/11/static/errcodes-appendix.html.

User-defined exceptions included an example that demonstrates how to declare a user-defined exception in a package. The following example uses the same basic structure, but adds a PRAGMA EXCEPTION_INIT declaration:

CREATE OR REPLACE PACKAGE ar AS
  overdrawn EXCEPTION;
  PRAGMA EXCEPTION_INIT (overdrawn, -20100);
  PROCEDURE check_balance(p_balance NUMBER, p_amount NUMBER);
END;

CREATE OR REPLACE PACKAGE BODY ar AS
   PROCEDURE check_balance(p_balance NUMBER, p_amount  NUMBER)
   IS
   BEGIN
       IF (p_amount > p_balance) THEN
         RAISE overdrawn;
       END IF;
    END;

The following procedure (purchase) calls the check_balance procedure. If p_amount is greater than p_balance, check_balance raises an exception, and purchase catches the ar.overdrawn exception.

CREATE PROCEDURE purchase(customerID int, amount NUMERIC)
AS
  BEGIN
     ar.check_ balance(getcustomerbalance(customerid), amount);
       record_purchase(customerid, amount);
  EXCEPTION
     WHEN ar.overdrawn THEN
      DBMS_OUTPUT.PUT_LINE ('This account is overdrawn.') ;
      DBMS_OUTPUT.PUT_LINE ('SQLCode :'||SQLCODE||' '||SQLERRM );
END;

When ar.check_balance raises an exception, execution jumps to the exception handler defined in purchase.

EXCEPTION
     WHEN ar.overdrawn THEN
      DBMS_OUTPUT.PUT_LINE ('This account is overdrawn.') ;
      DBMS_OUTPUT.PUT_LINE ('SQLCode :'||SQLCODE||' '||SQLERRM );

The exception handler returns an error message, followed by SQLCODE information:

This account is overdrawn.
SQLCODE: -20100 User-Defined Exception

The following example demonstrates how to use a predefined exception. The code creates a more meaningful name for the no_data_found exception. If the given customer does not exist, the code catches the exception, calls DBMS_OUTPUT.PUT_LINE to report the error, and then re-raises the original exception:

CREATE OR REPLACE PACKAGE ar AS
  overdrawn EXCEPTION;
  PRAGMA EXCEPTION_INIT (unknown_customer, no_data_found);
  PROCEDURE check_balance(p_customer_id NUMBER);
END;

CREATE OR REPLACE PACKAGE BODY ar AS
   PROCEDURE check_balance(p_customer_id NUMBER)
   IS
   DECLARE
     v_balance NUMBER;
   BEGIN
     SELECT balance INTO v_balance FROM customer
       WHERE cust_id = p_customer_id;
   EXCEPTION WHEN unknown_customer THEN
     DBMS_OUTPUT.PUT_LINE('invalid customer id');
     RAISE;
   END;