Re: cancel an insert within the trigger?

From: Rene Nyffenegger <rene.nyffenegger_at_gmx.ch>
Date: 21 Sep 2004 15:47:21 GMT
Message-ID: <slrncl0j67.28k.rene.nyffenegger@zhnt60m34.netarchitects.com>

In article <f858471c.0409210721.3a828218_at_posting.google.com>, Ben Graham wrote:
> avanrossem_at_hotmail.com (Andre) wrote in message news:<4d32d1be.0409210219.26642641_at_posting.google.com>...

>> Hello all,
>> 
>> I have created an insert trigger:
>> If I do a count on the table and this count results in a 1 or higher I
>> would not insert the record. (of_id is not the primary key)
>> 

> CREATE OR REPLACE TRIGGER iu_cli BEFORE insert or update on client
> FOR EACH ROW
> DECLARE
> CC number;
> BEGIN
> IF INSERTING
> THEN
> select count(*) into CC from client WHERE of_id = :new.of_id;
> If CC > 0 then
> --do not insert
> raise_application_error(-20000,'Invalid of_id. Your message here');
> end if;
> END IF;
> END;
> /

That's most probably not what the OP wants

Consider

create table client (
  of_id number,
  foooo number
);   

CREATE OR REPLACE TRIGGER iu_cli BEFORE insert or update on client FOR EACH ROW
DECLARE
CC number;
BEGIN
   IF INSERTING
   THEN
    select count(*) into CC from client WHERE of_id = :new.of_id;     If CC > 0 then

      --do not insert
       raise_application_error(-20000,'Invalid of_id. Your message here');

    end if;
   END IF;
END;
/

• Run the following PL/SQL block
• simultanously in two SQL*Plus
• sessions

begin
  for i in 1 .. 50000 loop
    begin

      insert into client values 
      (mod(i,20), i);

    exception when others then null;
    end;
  end loop;
end;
/

commit;

• Then....

select count(*), of_id from client group by of_id;

  COUNT(*) OF_ID
---------- ----------

         2          0
         2          1
         2          2
         2          3
         2          4
         2          5
         2          6
         2          7
         2          8
         2          9
         2         10
         2         11
         2         12
         2         13
         2         14
         2         15
         2         16
         2         17
         2         18
         2         19

> ...or create an unique constraint on client.of_id:
>
> alter table client
> add constraint client_of_id_uni
> unique (of_id);

Definitely the better approach.

Rene

-- 
  Rene Nyffenegger
  http://www.adp-gmbh.ch/

Received on Tue Sep 21 2004 - 10:47:21 CDT