serial as FK ?

Oleg Bartunov wrote:

Hi there,

what's wrong to use SERIAL as FK without explicit PRIMARY KEY or UNIQUE ?

qq=# create table t1( id serial);
NOTICE: CREATE TABLE will create implicit sequence "t1_id_seq" for
"serial" column "t1.id"
CREATE TABLE
qq=# create table t2( id2 int4 references t1(id));
ERROR: there is no unique constraint matching given keys for referenced
table "t1"

btw, Richard, I noticed this problem when looked into your example database
http://www.archonet.com/pgdocs/chap-exdb.html#EXAMPLE-TABLES

Ah - IIRC there *was* nothing wrong with it when those notes were
written (and I need to update them, clearly). Back then SERIAL implied
UNIQUE too, but that was changed (in 7.3 I believe).

--
Richard Huxton
Archonet Ltd

On Mon, 28 Feb 2005, Richard Huxton wrote:

Oleg Bartunov wrote:

Hi there,

what's wrong to use SERIAL as FK without explicit PRIMARY KEY or UNIQUE ?

qq=# create table t1( id serial);
NOTICE: CREATE TABLE will create implicit sequence "t1_id_seq" for
"serial" column "t1.id"
CREATE TABLE
qq=# create table t2( id2 int4 references t1(id));
ERROR: there is no unique constraint matching given keys for referenced
table "t1"

btw, Richard, I noticed this problem when looked into your example database
http://www.archonet.com/pgdocs/chap-exdb.html#EXAMPLE-TABLES

Ah - IIRC there *was* nothing wrong with it when those notes were written
(and I need to update them, clearly). Back then SERIAL implied UNIQUE too,
but that was changed (in 7.3 I believe).

There are also some problems in examples. I think your notes are rather
useful.

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83

On Mon, 28 Feb 2005, Oleg Bartunov wrote:

what's wrong to use SERIAL as FK without explicit PRIMARY KEY or UNIQUE ?

Serial isn't enough to guarantee uniqueness as required by foreign keys.

On Mon, 28 Feb 2005, Stephan Szabo wrote:

On Mon, 28 Feb 2005, Oleg Bartunov wrote:

what's wrong to use SERIAL as FK without explicit PRIMARY KEY or UNIQUE ?

Serial isn't enough to guarantee uniqueness as required by foreign keys.

you're certainly right !

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83