| Trigger [message #71857] |
Wed, 22 January 2003 09:31  |
Pratibha
Messages: 29
Registered: November 2001
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Junior Member |
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Hai
I do understand somewhat about triggers.
Here ,I got one question,what it is
For what purpose,we are using triggers?
Thank you
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| Re: Trigger [message #71898 is a reply to message #71857] |
Wed, 29 January 2003 15:24  |
Pratibha
Messages: 29
Registered: November 2001
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Junior Member |
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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
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| Re: Trigger [message #71901 is a reply to message #71857] |
Thu, 30 January 2003 06:42 |
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Mahesh Rajendran
Messages: 10707
Registered: March 2002
Location: oracleDocoVille
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Senior Member
Account Moderator |
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before every insert in table order_detail, this trigger is fired.
it checks whether a particulr orno already exists.
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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
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correct code should be
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if :new.orno='o001'
then raise_application_error
...
...
</hr>
now you check whether the orno that is CURRENTLY INSERTED equal to 'o001'
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