Is it safe to use DEFAULT currval()
I've got a table, and I'm trying to track changes to it, but can't do it via a
primary key including a revision-number (historical reasons).
CREATE TABLE foo (
id SERIAL,
blah text,
tracking int4 DEFAULT currval('foo_id_seq')
PRIMARY KEY (id)
);
I'm actually setting the DEFAULT on tracking using ALTER TABLE after the
event.
Now - it works, but is that a design feature or just luck?
It's convenient that tracking = id of the first entry, but not vital, so I can
always use a separate sequence if needs be.
--
Richard Huxton
Archonet Ltd
Richard Huxton <dev@archonet.com> writes:
CREATE TABLE foo (
id SERIAL,
blah text,
tracking int4 DEFAULT currval('foo_id_seq')
PRIMARY KEY (id)
);
Now - it works, but is that a design feature or just luck?
You're essentially assuming that the column expressions for an INSERT
will be evaluated left-to-right. That's true at the moment, and I don't
see any foreseeable reason why we'd change it, but it surely is an
implementation dependency that could bite you someday.
regards, tom lane
On Saturday 27 September 2003 18:40, Tom Lane wrote:
Richard Huxton <dev@archonet.com> writes:
CREATE TABLE foo (
id SERIAL,
blah text,
tracking int4 DEFAULT currval('foo_id_seq')
PRIMARY KEY (id)
);Now - it works, but is that a design feature or just luck?
You're essentially assuming that the column expressions for an INSERT
will be evaluated left-to-right. That's true at the moment, and I don't
see any foreseeable reason why we'd change it, but it surely is an
implementation dependency that could bite you someday.
I feared as much. Ah well, use nextval(), a different sequence or write a
trigger I suppose.
--
Richard Huxton
Archonet Ltd