A DequeueCondition is specified as a Boolean expression using syntax similar to the WHERE clause of a SQL query. This Boolean expression can include conditions on message properties, user data properties (object payloads only), and PL/SQL or SQL functions (as specified in the WHERE clause of a SQL query). To specify dequeue conditions on a message payload (object payload), use attributes of the object type in clauses. You must prefix each attribute with tab.user_data as a qualifier to indicate the specific column of the queue table that stores the payload. The DequeueCondition parameter cannot exceed 4000 characters. If more than one message satisfies the dequeue condition, the order of dequeuing is undetermined.

Reference

OracleQueueDequeueOptions Class
OracleQueueDequeueOptions Members