how to daclare queue data-structure in oracle? - oracle

Question

is There Any Way to Declare a Queue Data Structure Which be Accessible Globally in Oracle or in a Specific Schema?
With Globally i Mean be Accessible in All Procedures of Database or Specific Schema
edited :
i find out i can make FIFO QUEUE by package. so i wrote a code but i get error. any one know why i get this error?
package spec:
CREATE OR REPLACE PACKAGE HR.TEST_PACKAGE IS
PROCEDURE ADDQ (TABLE_NAME VARCHAR2);
FUNCTION DELQ RETURN VARCHAR2;
END TEST_PACKAGE;
/
package body:
CREATE OR REPLACE PACKAGE BODY HR.TEST_PACKAGE IS
REAR NUMBER := 0;
FRONT NUMBER := 0;
TYPE QUEUE_TYPE IS VARRAY(10) OF VARCHAR2(15);
QUEUE_ARRAY QUEUE_TYPE;
PROCEDURE ADDQ (TABLE_NAME VARCHAR2) IS
BEGIN
REAR := (REAR+1) MOD 10;
IF (REAR = 0) THEN
REAR := 10;
END IF;
QUEUE_ARRAY(REAR) := TABLE_NAME;
END ADDQ;
FUNCTION DELQ RETURN VARCHAR2 IS
BEGIN
IF (FRONT = REAR) THEN
RETURN 'EMPTY';
ELSE
FRONT := (FRONT + 1) MOD 10;
IF (FRONT = 0) THEN
front := 10;
END IF;
RETURN QUEUE_ARRAY(FRONT);
END IF;
END DELQ;
END TEST_PACKAGE;
/
when i run this example code:
create or replace procedure hr.test is
begin
hr.test_package.addq('a');
hr.test_package.addq('b');
dbms_output.put_line(hr.test_package.delq);
end test;
i get this error:
ORA-06531: Reference to uninitialized collection
06531. 00000 - "Reference to uninitialized collection"
*Cause: An element or member function of a nested table or varray
was referenced (where an initialized collection is needed)
without the collection having been initialized.
*Action: Initialize the collection with an appropriate constructor
or whole-object assignment.
and this error occur when wants to run this part of a code:
QUEUE_ARRAY(REAR) := TABLE_NAME;

Answer 1

Problem Solved. following code will declare a FIFO QUEUE in oracle.
the addq procedure will insert in queue and delq function will delete and return a value from queue.
package spec:
CREATE OR REPLACE PACKAGE HR.TEST_PACKAGE IS
PROCEDURE ADDQ (TABLE_NAME VARCHAR2);
FUNCTION DELQ RETURN VARCHAR2;
END TEST_PACKAGE;
/
package body:
CREATE OR REPLACE PACKAGE BODY HR.TEST_PACKAGE IS
REAR NUMBER := 0;
FRONT NUMBER := 0;
TYPE QUEUE_TYPE IS VARRAY(10) OF VARCHAR2(15);
QUEUE_ARRAY QUEUE_TYPE := QUEUE_TYPE() ;
PROCEDURE ADDQ (TABLE_NAME VARCHAR2) IS
BEGIN
REAR := (REAR+1) MOD 10;
IF (REAR = 0) THEN
REAR := 10;
END IF;
QUEUE_ARRAY.EXTEND;
QUEUE_ARRAY(REAR) := TABLE_NAME;
END ADDQ;
FUNCTION DELQ RETURN VARCHAR2 IS
BEGIN
IF (FRONT = REAR) THEN
RETURN 'EMPTY';
ELSE
FRONT := (FRONT + 1) MOD 10;
IF (FRONT = 0) THEN
front := 10;
END IF;
RETURN QUEUE_ARRAY(FRONT);
END IF;
END DELQ;
END TEST_PACKAGE;
/