trouble defining weakly defined ref cursor - sql

Question

I'm attempting to write a stored proc that takes in a number, n, and returns the first n results for a given query, exclusively locking those n rows. I'm a little new to SQL and I'm having a bit of difficulty matching data types correctly.
My package spec looks like this:
PACKAGE package IS
Type out_result_type is REF CURSOR;
PROCEDURE stored_proc
(in_n IN NUMBER DEFAULT 10,
out_list IN OUT out_result_type);
I then define the cursor in the procedure body, like so:
CURSOR OUT_RESULT_TYPE IS
SELECT a.id
FROM schema.table a
WHERE (some conditions) AND rownum <= in_n;
A bit later on I then try to extract the results of the cursor into the output variable:
OPEN OUT_RESULT_TYPE;
FETCH OUT_RESULT_TYPE INTO out_list; -- error on this line
CLOSE OUT_RESULT_TYPE;
But alas this code doesn't compile; oracle complains that out_list has already been defined with a conflicting data type. Any idea how I can resolve this issue? It's driving me crazy!
Thanks in advance.

Answer 1

CREATE OR REPLACE PACKAGE pkg_test
AS
TYPE tt_cur IS REF CURSOR;
PROCEDURE prc_cur (retval OUT tt_cur);
END;
CREATE OR REPLACE PACKAGE BODY pkg_test
AS
PROCEDURE prc_cur (retval OUT tt_cur)
AS
BEGIN
OPEN retval
FOR
SELECT *
FROM dual;
END;
END;
If you want to lock, use:
CREATE OR REPLACE PACKAGE BODY pkg_test
AS
PROCEDURE prc_cur (retval OUT tt_cur)
AS
BEGIN
OPEN retval
FOR
SELECT a.id
FROM schema.table a
WHERE (some conditions)
AND rownum <= in_n
ORDER BY
column
-- Never forget ORDER BY!
FOR UPDATE;
END;
END;

Answer 2

Two remarks:
A cursor doesn't lock.
You don't have to do Type out_result_type is REF CURSOR;, use default type sys_refcursor. See here: Oracle - How to have an out ref cursor parameter in a stored procedure?

Answer 3

Your out_list must be of wrong type. Consider (script run on 10.2.0.3):
CREATE TABLE t AS SELECT ROWNUM ID FROM all_objects WHERE ROWNUM <= 100;
CREATE OR REPLACE PACKAGE cursor_pck AS
TYPE out_result_type is REF CURSOR;
PROCEDURE stored_proc (p_in IN NUMBER DEFAULT 10,
p_out_list IN OUT out_result_type);
END cursor_pck;
/
If you want to select and lock the rows at the same time you would use the FOR UPDATE clause:
CREATE OR REPLACE PACKAGE BODY cursor_pck AS
PROCEDURE stored_proc (p_in IN NUMBER DEFAULT 10,
p_out_list IN OUT out_result_type) IS
BEGIN
OPEN p_out_list FOR SELECT a.id FROM t a WHERE ROWNUM <= p_in FOR UPDATE;
END stored_proc;
END cursor_pck;
/
With the following setup, you will call the procedure like this:
SQL> SET SERVEROUTPUT ON;
SQL> DECLARE
2 l_cursor cursor_pck.out_result_type;
3 l_id t.id%TYPE;
4 BEGIN
5 cursor_pck.stored_proc(3, l_cursor);
6 LOOP
7 FETCH l_cursor INTO l_id;
8 EXIT WHEN l_cursor%NOTFOUND;
9 dbms_output.put_line(l_id);
10 END LOOP;
11 END;
12 /
1
2
3
PL/SQL procedure successfully completed

Answer 4

This is not going to work the way it's written, because
out_list expects a cursor, not a cursor result.
The name out_result_type is already used for a type, so you can't redefine it to be a cursor in the same scope.

Answer 5

Oracle provides a pre-defined weak reference cursor: sys_refcursor. In usage it would look like:
CREATE OR REPLACE PACKAGE pkg_test
AS
PROCEDURE prc_cur (p_retval OUT sys_refcursor,
p_lookup IN VARCHAR2);
END pkg_test;
CREATE OR REPLACE PACKAGE BODY pkg_test
AS
PROCEDURE prc_cur(p_retval OUT sys_refcursor
p_lookup IN VARCHAR2)
IS
BEGIN
OPEN retval FOR SELECT a.value
FROM tblname a
WHERE a.id <= p_lookup;
END prc_cur;
END pkg_test;
This saves you the trouble of needing to declare a type. The sys_refcursor is a pointer to a result set from an open cursor. If you are familiar with Java, it's the same concept as the java.sql.ResultSet object which provides a way to get at the results of a query.