From: ktm@rice.edu <ktm@rice.edu>
To: Francisco Calderón <fjcalderon@gmail.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Problem with sequence increment
Date: Wed, 25 Jan 2012 08:31:49 -0600
Message-ID: <20120125143149.GF10228@aart.rice.edu> (raw)
In-Reply-To: <CAFVakMosc3T5WmhQqwDLQEkPRhChA9KoOUVQKGUR-3xwXBVOSg@mail.gmail.com>
References: <CAFVakMosc3T5WmhQqwDLQEkPRhChA9KoOUVQKGUR-3xwXBVOSg@mail.gmail.com>
On Wed, Jan 25, 2012 at 09:42:05AM -0430, Francisco Calderón wrote:
> Hello,
>
> I am having a situation with postgresql 8.3, i have two tables, ta and tb,
> with a relation "one tb has many ta" and... well, i will let the SQL talk
> for me ;)
>
> -----------SQL-----------
> CREATE TABLE tb
> (
> id serial NOT NULL,
> descripcion character varying(200) NOT NULL,
> CONSTRAINT tb_pkey PRIMARY KEY (id)
> )
> WITH (OIDS=FALSE);
> INSERT INTO tb (descripcion) values ('desc 1');
> INSERT INTO tb (descripcion) values ('desc 2');
> CREATE TABLE ta
> (
> id serial NOT NULL,
> descripcion character varying(200),
> tb_id integer default null,
> CONSTRAINT ta_pkey PRIMARY KEY (id),
> CONSTRAINT ta_tb_id FOREIGN KEY (tb_id)
> REFERENCES tb (id) MATCH SIMPLE
> ON UPDATE NO ACTION ON DELETE NO ACTION
> )
> WITH (OIDS=FALSE);
>
> When i make an insert like this:
>
> INSERT INTO ta (descripcion, tb_id) values ('prueba', 0);
>
> we can expect this error:
>
> ERROR: insert or update on table "ta" violates foreign key constraint
> "ta_tb_id"
> DETAIL: Key (tb_id)=(0) is not present in table "tb".
>
> and that is what i am getting but the unusual situation is the sequence
> "ta_id_seq" is incrementing every time i get the "violates foreign key
> constraint" error and i think this is not a good behavior, what do you
> think?
>
That is how sequences work. If you want different behavior, use another
process or method to produce a sequential count. Hint, it will involve
a lot of locking and be much slower than a sequence. It would be better
to have your application handle gaps in the sequence.
Regards,
Ken
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To: pgsql-sql@postgresql.org
Cc: ktm@rice.edu, fjcalderon@gmail.com
Subject: Re: Problem with sequence increment
In-Reply-To: <20120125143149.GF10228@aart.rice.edu>
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