Re: PRIMARY KEY

Phillip Smith wrote:
> If you actually need to know the value of N_GEN in your ASP
> application, you will need to query the database first and select the
> NEXTVAL from the sequence that the "serial" data type will create,
> then use that returned value in your insert - ie, DON'T exclude it
> from the insert, otherwise it will default to NEXTVAL again and return
> a different value.
>
> The only catch with this is that you most likely won't end up with
> contiguous values in this column - ie, if a user cancels after you
> seect nextval, but before you insert - the value of the sequence has
> already increased, and will be increased again before returning a
> value when you next select nextval
>

That's precisely why I would not use the nextval call, you might end up
with gaps. Moreover you are making 2 database calls instead of one.
But then again, if your application needs to know the value you can't
really avoid using nextval (good thing it's concurrency proof)

Mario

Phillip Smith wrote:
> If you actually need to know the value of N_GEN in your ASP
> application, you will need to query the database first and select the
> NEXTVAL from the sequence that the "serial" data type will create,
> then use that returned value in your insert - ie, DON'T exclude it
> from the insert, otherwise it will default to NEXTVAL again and return
> a different value.
>
> The only catch with this is that you most likely won't end up with
> contiguous values in this column - ie, if a user cancels after you
> seect nextval, but before you insert - the value of the sequence has
> already increased, and will be increased again before returning a
> value when you next select nextval
>
> Cheers,
> ~p
>
> On Wed, 2007-03-07 at 12:57 +0100, M.P.Dankoor wrote:
>> Hello,
>>
>> Is it possible to redesign your table as follows:
>>
>> create table Mod48_00_2007 (
>> ID text,
>> N_GEN serial not null,
>> FORMSTORE text,
>> COD_NOTATIO text,
>> PA_COGNOME text,
>> constraint pk_Mod48_00_2007 primary key (N_GEN)
>> );
>>
>> Your insert simply becomes:
>> INSERT INTO MOD48_00_2007 (ID, FORMSTORE, COD_NOTAIO, PA_COGNOME)
>> VALUES ('192168217200737122012', '', '00128', 'DE MARTINIS')
>>
>> Do note that you do not refer to the N_GEN column, it will use the
>> next value, please refer to
>> http://www.postgresql.org/docs/8.1/interactive/datatype.html#DATATYPE-SERIAL
>> for more information.
>>
>> Mario
>>
>> Shavonne Marietta Wijesinghe wrote:
>>> Hello
>>>
>>> I have created a table
>>> CREATE TABLE MOD48_00_2007 ( ID text, N_GEN int PRIMARY KEY,
>>> FORMSTORE text, COD_NOTAIO text, PA_COGNOME text);
>>>
>>> And i insert the rows via a form in ASP. When the form loads i have
>>> a functin that goes and gets the value of the field N_GEN adds 1 to
>>> it and shows it to the user.
>>> The problem is when i have 2 users working at the same time.
>>>
>>> For example the last value in my field N_GEN is 2
>>> When both the users A and B loads the form (ASP page) it sees N_GEN
>>> = 3 :)
>>>
>>> So they fill in the form and user A clicks on the button OK and the
>>> record has been inserted with N_GEN = 3. But when the user B clicks
>>> on the button the record is not inserted because it has the same key
>>> "3"
>>>
>>> INSERT INTO MOD48_00_2007 (ID, N_GEN, FORMSTORE, COD_NOTAIO,
>>> PA_COGNOME) VALUES ('192168217200737122012', '3', '', '00128', 'DE
>>> MARTINIS')
>>>
>>> Is there any way i can do this automatically? i mean maybe i have to
>>> use someother property instead of "Primary Key" ??
>>>
>>> Thanks
>>>
>>> Shavonne Wijesinghe
>>>
>>
>
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