Insert row to table B before updating it in table A - sql

Question

I have a table called applications and a table called application_history. I want to keep a history of applications and had the idea of using a trigger whenever a row gets updated in the applications table to copy that row to application_history before it is actually updated.
At the moment, I've written this code out from another SO post:
create or replace
trigger APPLICATION_UPDATE_TRG
BEFORE UPDATE ON TBL_APPLICATIONS
FOR EACH ROW
DECLARE
CURSOR curAppHistory IS
SELECT record_number, job_id, submitted_date, status_id, id
FROM tbl_application
WHERE id = :old.id;
vRowAppHistory curAppHistory%ROWTYPE;
BEGIN
OPEN curAppHistory;
FETCH curAppHistory INTO vRowAppHistory;
CLOSE curAppHistory;
INSERT INTO tbl_application_history
(record_number, job_id, submitted_date, status_id, application_id)
VALUES (vRowAppHistory.record_number, vRowAppHistory.job_id, vRowAppHistory.submitted_date,
vRowAppHistory.status_id, vRowAppHistory.id);
END;
However, it's not properly compiling. SQL Developer throws out 3 errors about commands not properly ended and statements being ignored.
What's the proper way to do this?
Edit: The errors:
Error(2,10): PLS-00341: declaration of cursor 'CURAPPHISTORY' is incomplete or malformed
Error(3,5): PL/SQL: SQL Statement ignored
Error(4,12): PL/SQL: ORA-00942: table or view does not exist
Error(6,18): PL/SQL: Item ignored
Error(9,3): PL/SQL: SQL Statement ignored
Error(9,28): PLS-00320: the declaration of the type of this expression is incomplete or malformed
Error(11,3): PL/SQL: SQL Statement ignored
Error(14,29): PLS-00320: the declaration of the type of this expression is incomplete or malformed
Error(14,44): PL/SQL: ORA-00984: column not allowed here

Answer 1

Error(4,12): PL/SQL: ORA-00942: table or view does not exist
A typo? You specified two different tables here.
BEFORE UPDATE ON TBL_APPLICATIONS
FROM tbl_application
Anyway, you'll get ORA-04091 with this trigger. Similar test case:
SYSTEM#dwal> create table t (key number primary key, value varchar2(10));
Table created.
SYSTEM#dwal> insert into t values (1, 'abcdef');
1 row created.
SYSTEM#dwal> insert into t values (2, 'ghijkl');
1 row created.
SYSTEM#dwal> commit;
Commit complete
SYSTEM#dwal> ed
Wrote file S:\\tools\buffer.sql
1 create or replace trigger tt
2 before update on t for each row
3 declare
4 cursor c is
5 select key, value
6 from t
7 where key = :old.key;
8 v c%rowtype;
9 begin
10 open c;
11 fetch c into v;
12 close c;
13 dbms_output.put_line(v.value);
14* end;
09:58:51 SYSTEM#dwal> /
Trigger created.
SYSTEM#dwal> update t set value = '123';
update t set value = '123'
*
ERROR at line 1:
ORA-04091: table SYSTEM.T is mutating, trigger/function may not see it
ORA-06512: at "SYSTEM.TT", line 3
ORA-06512: at "SYSTEM.TT", line 8
ORA-04088: error during execution of trigger 'SYSTEM.TT'
You should probably do it like this:
INSERT INTO tbl_application_history
(record_number, job_id, submitted_date, status_id, application_id)
VALUES
(:old.record_number, :old.job_id, :old.submitted_date, :old.status_id, :old.id);
The whole trigger would be a single insert statement in this case:
SYSTEM#dwal> create table t_log (key number, value varchar2(10));
Table created.
SYSTEM#dwal> ed
Wrote file S:\\tools\buffer.sql
1 create or replace trigger tt
2 before update on t for each row
3 begin
4 insert into t_log values (:old.key, :old.value);
5* end;
SYSTEM#dwal> /
Trigger created.
SYSTEM#dwal> update t set value = '123';
2 rows updated.
SYSTEM#dwal> commit;
Commit complete.
SYSTEM#dwal> select * from t_log;
KEY VALUE
---------- ----------
1 abcdef
2 ghijkl
SYSTEM#dwal> select * from t;
KEY VALUE
---------- ----------
1 123
2 123