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Thread: Re: Primary Key with serial the solution?

Re: Primary Key with serial the solution?

From
"x asasaxax"
Date:
How about if i do this inside a procedure:

SELECT setval('sequence',(SELECT max(id) FROM table)) INTO variable;
insert into table values(variable, ..., ...);  ?

Will this be transactional? Cause, they say that setval is a command that its transactional. Using this way i

don´t will need to use a sequence anymore. Is that correct?


Thanks you all.


2008/3/31, x asasaxax <xanaruto@gmail.com>:
can anyone do a example for me.. an explain how it works?
 
Thanks a lot

 
2008/3/29, Berend Tober <btober@ct.metrocast.net>:
x asasaxax wrote:
>    I have the following table    create table product(cod serial, user_cod
> bigint, constraint product_fk Foreign Key(user_cod) references user(cod),
> constraint product_pk Primary Key(cod, user_cod));
>
> What i want to happend is that:
> user_cod            cod
> 1                         1
> 1                         2
> 1                         3
> 2                         1
> 3                         1
> 3                         2
>
> Can serial do that? ...

No.

> ...what can  i do to make this happen?


http://archives.postgresql.org/pgsql-general/2006-08/msg00744.php




Re: Primary Key with serial the solution?

From
Craig Ringer
Date:
x asasaxax wrote:
> How about if i do this inside a procedure:
>
> SELECT setval('sequence',(SELECT max(id) FROM table)) INTO variable;
> insert into table values(variable, ..., ...);  ?
>
> Will this be transactional? Cause, they say that setval is a command
> that its transactional. Using this way i
> don´t will need to use a sequence anymore. Is that correct?

If somebody else INSERTs a record between your first and second
statements, it will get the first free value in the sequence so your
INSERT will fail with a unique check voliation. Assuming there's a
unique constraint involved, which I assume there is given your use of a
sequence.

Why do you want to do this? Sequences are designed so that you can just:

INSERT INTO table VALUES ( nextval('sequence'), ..., ...)

or set the DEFAULT on the generated value field such that it calls
nextval('sequence') if the user just does:

INSERT INTO table VALUES ( DEFAULT, ... , ... )

or uses a named-field INSERT and omits the sequence column entirely.

Why not use them that way?

Is there something you're trying to achieve that sequences aren't doing
the job for - like, say, "gap-less" generated values? If that's the
problem please search the archives as it's already been discussed to
death even in the short time I've been a list member.

--
Craig Ringer