Thread: Problem with sequence increment

Problem with sequence increment

From

Francisco Calderón

Date:

25 January 2012, 13:12:41

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?

Thanks in advance.
//
// Francisco J. Calderón S.
//

Re: Problem with sequence increment

From

Brice André

Date:

25 January 2012, 13:31:27

Hello,

This is a normal behaviour of the sequence. In case of rollback, a sequence is never decremented. Read the note at the end of this page for more info :
http://www.postgresql.org/docs/8.1/static/functions-sequence.html

Regards,
Brice

2012/1/25 Francisco Calderón <fjcalderon@gmail.com>

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?

Thanks in advance.
//
// Francisco J. Calderón S.
//

Re: Problem with sequence increment

From

"ktm@rice.edu"

Date:

25 January 2012, 13:32:06

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