If you need to get the actual "current value" without incrementing, try:
SELECT last_value FROM <sequence_name>;
This will return the last value returned from a nextval command directly
from the sequence properties in the system tables.
-----Original Message-----
From: Dan Langille [mailto:dan@langille.org]
Sent: Thursday, June 06, 2002 12:34 PM
To: Nicolas Nolst
Cc: pgsql-admin@postgresql.org; pgsql-general@postgresql.org
Subject: Re: [ADMIN] [GENERAL] performance issue using DBI
On 6 Jun 2002 at 17:14, Oliver Elphick wrote:
> On Thu, 2002-06-06 at 14:55, Joshua b. Jore wrote:u
> > Don't use currval since some other process might alter the
> > sequence between the time you call nextval and currval.
>
> This is wrong. currval() will always return the last serial assigned
in
> *the*same*session*. It is not affected by other users at all.
Folks, here's a short test which might help. Note the BEGIN.
$ psql testing
testing=# create sequence test;
CREATE
testing=# select currval('test');
ERROR: test.currval is not yet defined in this session
testing=# select setval('test', 1);
setval
--------
1
(1 row)
testing=# select currval('test');
currval
---------
1
(1 row)
testing=# select currval('test');
currval
---------
1
(1 row)
testing=# select currval('test');
currval
---------
1
(1 row)
testing=# select currval('test');
currval
---------
1
(1 row)
testing=#
Then, in another window, I did this:
$ psql testing
# select nextval('test');
nextval
---------
2
(1 row)
testing=# select nextval('test');
nextval
---------
3
(1 row)
testing=# select nextval('test');
nextval
---------
4
(1 row)
testing=#
Then back to the other window:
testing=# select currval('test');
currval
---------
1
(1 row)
testing=# select nextval('test');
nextval
---------
5
(1 row)
testing=#
cheers
FWIW: I always use nextval when looking for a new ID.
--
Dan Langille
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