| Trigger [message #71857] |
Wed, 22 January 2003 09:31  |
Pratibha
Messages: 29
Registered: November 2001
|
Junior Member |
|
|
Hai
I do understand somewhat about triggers.
Here ,I got one question,what it is
For what purpose,we are using triggers?
Thank you
|
|
|
|
|
|
| Re: Trigger [message #71898 is a reply to message #71857] |
Wed, 29 January 2003 15:24  |
Pratibha
Messages: 29
Registered: November 2001
|
Junior Member |
|
|
Thank u very much.
here,I have an example from one text book
some x-company would like to trap some data entry errors like entering quantity delivered is greater than quantity ordered.
create or replace trigger orders before insert on order_detail for each row
declare
orno order_detail.orderno%type;
begin
select orderno into orno from order_detail where quantity_ord<quantity_deld;
if orno='o001' then
raise_application_error(-20,001,'enter some other number');
end if;
end;
/
please explain me what is going in this trigger body
Thanks for your time
|
|
|
|
| Re: Trigger [message #71901 is a reply to message #71857] |
Thu, 30 January 2003 06:42 |
 |
Mahesh Rajendran
Messages: 10708
Registered: March 2002
Location: oracleDocoVille
|
Senior Member
Account Moderator |
|
|
before every insert in table order_detail, this trigger is fired.
it checks whether a particulr orno already exists.
----------------------------------------------------------------------
this trigger is have logical error.
it always checks for orno='o001'.
ie..if there is already an orno='o001' inserted,
then, TRIGGER WILL NOT ALLOW U TO INSERT ANY RECORD.
becuase u are checking if orno='o001' is present in table
IRRELEVANT of wat u insert
----------------------------------------------------------------------
correct code should be
----------------------------------------------------------------------
if :new.orno='o001'
then raise_application_error
...
...
</hr>
now you check whether the orno that is CURRENTLY INSERTED equal to 'o001'
|
|
|
|
] 
Blog
Search
Help
Members
Register
Login
Home
