Advanced Queuing - Oracle

Dequeue Features
Scenario
In the customer service component of the BooksOnLine example, messages from
different databases arrive in the customer service queues, indicating the state of the
message. The customer service application monitors the queues and whenever there
is a message about a customer order, it updates the order status in the order_
status_table. The application uses the listen call to monitor the different
queues. Whenever there is a message in any of the queues, it dequeues the message
and updates the order status accordingly.
PL/SQL (DBMS_AQADM Package): Example Code
CODE (in tkaqdocd.sql)
/* Update the status of the order in the order status table: */
CREATE OR REPLACE PROCEDURE update_status(
new_status IN VARCHAR2,
order_msg IN BOLADM.ORDER_TYP)
IS
old_status VARCHAR2(30);
dummy NUMBER;
BEGIN
BEGIN
/* Query old status from the table: */
SELECT st.status INTO old_status FROM order_status_table st
WHERE st.customer_order.orderno = order_msg.orderno;
/* Status can be 'BOOKED_ORDER', 'SHIPPED_ORDER', 'BACK_ORDER'
and 'BILLED_ORDER': */
IF new_status = 'SHIPPED_ORDER' THEN
IF old_status = 'BILLED_ORDER' THEN
return; /* message about a previous state */
END IF;
ELSIF new_status = 'BACK_ORDER' THEN
IF old_status = 'SHIPPED_ORDER' OR old_status = 'BILLED_ORDER' THEN
return; /* message about a previous state */
END IF;
END IF;
/* Update the order status: */
UPDATE order_status_table st
SET st.customer_order = order_msg, st.status = new_status;
A Sample Application Using AQ 8-91