Update previous record version during Oracle insert trigger - sql

Question

This is my insert trigger on Table_A where I store parameters to my system. When I do insert to the table, I want to change end_date of last record in order to keep record versioning.
create or replace trigger parameter_version
before insert
on parameters
for each row
declare
v_is_exist number := 0;
v_rowid rowid;
begin
select count(*) into v_is_exist from parameters where name = :new.name; -- check if parameter exist
select rowid into v_rowid from parameters where name = :new.name and end_date is null; -- record rowid, which sholud be changed
if v_is_exist <> 0 then
set end_date = :new.start_date - 1
end if;
end;
Situation in table before insert is:
| id | name | value | start_date | end_date |
-----------------------------------------------
| 1 |Par_A | 10 | 2016-09-01 | 2016-10-01 |
-----------------------------------------------
| 2 |Par_A | 20 | 2016-10-02 | 2016-10-03 |
-----------------------------------------------
| 3 |Par_A | 30 | 2016-10-05 | <null> |
-----------------------------------------------
Record with id=3 should set end_date on :new_start_date - 1 (close version) and in inserting record I have a next param version with start_date = sysdate.
I've got an ORA-04091 error 'table name is mutating, trigger/function may not see it'.
I know that this case is hard and probably impossible but maybe someone know the solution?
Or maybe exists another solution that case?

Answer 1

You can handle this with an After Statement trigger with the LEAD Analytic Function:
DROP TABLE demo;
CREATE TABLE demo( id NUMBER
, name VARCHAR2( 30 )
, VALUE NUMBER
, start_date DATE
, end_date DATE
);
INSERT INTO demo( id, name, VALUE, start_date, end_date )
VALUES ( 1, 'Par_A', 10, TO_DATE( '2016-09-01', 'YYYY-MM-DD' ), TO_DATE( '2016-10-01', 'YYYY-MM-DD' ) );
INSERT INTO demo( id, name, VALUE, start_date, end_date )
VALUES ( 2, 'Par_A', 20, TO_DATE( '2016-10-02', 'YYYY-MM-DD' ), TO_DATE( '2016-10-04', 'YYYY-MM-DD' ) );
INSERT INTO demo( id, name, VALUE, start_date )
VALUES ( 3, 'Par_A', 30, TO_DATE( '2016-10-05', 'YYYY-MM-DD' ) );
INSERT INTO demo( id, name, VALUE, start_date )
VALUES ( 4, 'Par_A', 40, TO_DATE( '2016-10-07', 'YYYY-MM-DD' ) );
INSERT INTO demo( id, name, VALUE, start_date )
VALUES ( 5, 'Par_A', 50, TO_DATE( '2016-10-11', 'YYYY-MM-DD' ) );
COMMIT;
SELECT id
, name
, start_date
, end_date
, LEAD( start_date ) OVER( PARTITION BY name ORDER BY start_date ) - 1 AS new_date
FROM demo
WHERE end_date IS NULL
ORDER BY id;
CREATE OR REPLACE TRIGGER demo_aius
AFTER INSERT OR UPDATE
ON demo
REFERENCING NEW AS new OLD AS old
DECLARE
CURSOR c_todo
IS
SELECT id, new_date
FROM (SELECT id
, name
, start_date
, end_date
, LEAD( start_date ) OVER( PARTITION BY name ORDER BY start_date ) - 1 AS new_date
FROM demo
WHERE end_date IS NULL)
WHERE new_date IS NOT NULL;
BEGIN
FOR rec IN c_todo
LOOP
UPDATE demo
SET end_date = rec.new_date
WHERE id = rec.id;
END LOOP;
END demo_aius;
/
INSERT INTO demo( id, name, VALUE, start_date )
VALUES ( 6, 'Par_A', 60, TO_DATE( '2016-10-15', 'YYYY-MM-DD' ) );
COMMIT;
SELECT id
, name
, start_date
, end_date
FROM demo
ORDER BY id;
Like the Script shows, such an Update can even handle multiple missing end dates, in case the trigger was accidentally disabled. The "PARTITION BY name" part makes sure that it also functions after complex insert statements.
BtW I agree that Autonomous Transactions in triggers are a last resort. I try to avoid triggers in general by controlling the User Interface and putting all such functionality in packages.

Answer 2

Try something like this:
create or replace trigger parameter_version
before insert
on parameters
for each row
begin
/*Don't care if there's 0 rows updated */
update parameters
set end_date = :new.start_date - 1
where name = :new.name and end_date is null;
:new.end_date := null;
end;