Implicit conversion of date field in a pl/sql trigger? - oracle

Question

I need to develop a trigger in PL/SQL (Oracle) before INSERT.
In this table there is a column (cdat) of type DATE.
Let's say i do INSERT INTO myTbl (123,'12/05/2011');
In my trigger the :NEW.CDAT is converted in the final date system or it's still a varchar?
Do I need to do a TO_DATE(:NEW.CDAT) to get the date value?

Answer 1

:NEW.CDAT will be a date. The :new and :old variables in triggers are always the type of the destination field.
I wasn't able to find anything in the Oracle documentation that confirms my statement, but I was able to devise some experimental proof:
CREATE TABLE test2 (a DATE);
CREATE OR REPLACE TRIGGER bu_test2
BEFORE INSERT OR UPDATE
ON test2
FOR EACH ROW
DECLARE
PROCEDURE type_test(in_type DATE) IS
BEGIN
DBMS_OUTPUT.put_line('date');
END;
PROCEDURE type_test(in_type VARCHAR2) IS
BEGIN
DBMS_OUTPUT.put_line('varchar2');
END;
BEGIN
type_test(:new.a);
END;
INSERT INTO test2
VALUES ('24-Mar-2011');
Since type_test is overloaded, Oracle will choose which procedure to use based on the type being passed in. The results of this script are:
Table created.
Trigger created.
date
1 row created.

Answer 2

You need to do a conversion if your session parameter 'NLS_DATE_FORMAT' is not 'mm/dd/yyyy'.
For example:
create table myTbl (id number, cdat date);
select *
from nls_session_parameters ns
where ns.parameter = 'NLS_DATE_FORMAT';
PARAMETER VALUE
-------------------------------------------------------
NLS_DATE_FORMAT DD-MON-RR
In this case, without a to_Date you'll get an error:
insert into myTbl
values
(123, '12/05/2011');
ORA-01843: not a valid month
You can change this paramter at session level, system level, etc.
zep#dev> alter session set NLS_DATE_FORMAT = 'mm/dd/yyyy';
Session altered
select *
from nls_session_parameters ns
where ns.parameter = 'NLS_DATE_FORMAT';
PARAMETER VALUE
-------------------------------------------------------------------------------------
NLS_DATE_FORMAT mm/dd/yyyy
insert into myTbl
(id, cdat)
values
(123, '12/05/2011');
1 row inserted
zep#dev> select *
2 from myTbl;
ID CDAT
---------- -----------
123 05/12/2011
Test on a row level trigger
truncate table Mytbl;
alter session set NLS_DATE_FORMAT = 'DD-MON-RR';
create or replace trigger befins_myTbl
before insert on myTbl
for each row
declare
begin
-- demo
:new.cdat := :new.cdat + numtoyminterval(1,'YEAR');-- (demo trigger add 1 year )
end;
insert into myTbl
(id, cdat)
values
(123, '12/05/2011');
Output: ORA-01843: not a valid month
alter session set NLS_DATE_FORMAT = 'mm/dd/yyyy';
insert into myTbl
(id, cdat)
values
(123, '12/05/2011');
commit;
select *
from myTbl;
Output
ID CDAT
---------- -----------
123 12/05/2012