Return deleted rows in a cursor in PL/SQL - plsql

Question

I have a requirement where I want to return the deleted records in a sys_refcursor. I can retrieve the data in cursor before the delete statement but is there any way to retrieve them after a delete statement? I mean process will be like at first delete and then open sys_refcursor for fetching deleted records.

Answer 1

There are probably a few options, but one option would be to use RETURNING and BULK COLLECT. Here is a simple example.
CREATE TABLE t (
a NUMBER,
b VARCHAR2(10),
c DATE
);
INSERT INTO t VALUES (1, 'a', SYSDATE);
INSERT INTO t VALUES (2, 'b', SYSDATE);
INSERT INTO t VALUES (3, 'c', SYSDATE);
INSERT INTO t VALUES (4, 'd', SYSDATE);
INSERT INTO t VALUES (5, 'e', SYSDATE);
CREATE OR REPLACE TYPE tt AS OBJECT (
a NUMBER,
b VARCHAR2(10),
c DATE
);
CREATE OR REPLACE TYPE tt_tab AS TABLE OF tt;
DECLARE
v_tt_tab tt_tab;
v_tt tt;
v_cur SYS_REFCURSOR;
BEGIN
DELETE FROM t
WHERE a < 4
RETURNING tt(a, b, c) BULK COLLECT INTO v_tt_tab;
OPEN v_cur FOR
SELECT tt(a,
b,
c)
FROM TABLE(v_tt_tab);
LOOP
FETCH v_cur
INTO v_tt;
EXIT WHEN v_cur%NOTFOUND;
dbms_output.put_line(v_tt.a || ' ' || v_tt.b || ' ' || v_tt.c);
END LOOP;
CLOSE v_cur;
END;
/
/*
1 a 07-OCT-20
2 b 07-OCT-20
3 c 07-OCT-20
*/
By creating an object that matches the data we want to keep and a table of that object we can return that into a collection and then easily turn it back into a cursor using the TABLE function.
You need to be careful with how many rows you delete as you don't want to run out of memory. I would be cautious with this approach if you delete more than a few hundred rows.
Another suggestion might be to use a GTT, INSERT the rows you plan to delete and then delete from the first table using the GTT as your "key".
CREATE GLOBAL TEMPORARY TABLE t_gtt (
a NUMBER,
b VARCHAR2(10),
c DATE
);
DECLARE
v_tt_tab tt_tab;
v_tt tt;
v_cur SYS_REFCURSOR;
BEGIN
INSERT INTO t_gtt
SELECT *
FROM t
WHERE a < 4;
DELETE FROM t
WHERE EXISTS (SELECT NULL
FROM t_gtt
WHERE t_gtt.a = t.a);
OPEN v_cur FOR
SELECT tt(a,
b,
c)
FROM t_gtt;
LOOP
FETCH v_cur
INTO v_tt;
EXIT WHEN v_cur%NOTFOUND;
dbms_output.put_line(v_tt.a || ' ' || v_tt.b || ' ' || v_tt.c);
END LOOP;
CLOSE v_cur;
END;
/
This option is maybe better if you are planning to delete a large amount of rows. I used my tt object again, but you really don't need it. It just made looping to dump the contents of the SYS_REFCURSOR easier.