Advanced Queuing - Oracle

Dequeue Features
messages with the same correlation identifier, the ordering (enqueue order)
between messages may not be preserved on dequeue calls. The correlation identifier
cannot be changed between successive dequeue calls without specifying the first
message navigation option.
A dequeue condition is an expression that is similar in syntax to the WHERE clause
of a SQL query. Dequeue conditions are expressed in terms of the attributes that
represent message properties or message content. The messages in the queue are
evaluated against the conditions and a message that satisfies the given condition is
returned.
A default dequeue means that the first available message for the consumer of a
multiconsumer queue or the first available message in a single-consumer queue is
dequeued.
Note that dequeuing with correlation identifier, message identifier, or dequeue
condition will not preserve the message grouping property (see "Message
Grouping" on page 8-51 and "Message Navigation in Dequeue" on page 8-65 for
more information).
Scenario
In the BooksOnLine example, rush orders received by the East shipping site are
processed first. This is achieved by dequeuing the message using the correlation
identifier, which has been defined to contain the order type (rush/normal). For an
illustration of dequeuing using a message identifier, refer to the get_
northamerican_orders procedure discussed in the example under "Modes of
Dequeuing" on page 8-69.
PL/SQL (DBMS_AQADM Package): Example Code
CONNECT boladm/boladm;
/* Create procedures to dequeue RUSH orders */
create or replace procedure get_rushtitles(consumer in varchar2) as
deq_cust_data BOLADM.customer_typ;
deq_book_data BOLADM.book_typ;
deq_item_data BOLADM.orderitem_typ;
deq_msgid RAW(16);
dopt dbms_aq.dequeue_options_t;
mprop dbms_aq.message_properties_t;
deq_order_data BOLADM.order_typ;
qname varchar2(30);
no_messages exception;
A Sample Application Using AQ 8-59