Message-ID: <39B70836.94523C33@digital-mission.com>
Date: Wed, 06 Sep 2000 23:15:02 -0400
From: Mark Dzmura <mdz@digital-mission.com>
Organization: Digital Mission LLC
MIME-Version: 1.0
To: "pgsql-interfaces@postgreSQL.org" <pgsql-interfaces@postgreSQL.org>
Subject: obtaining primary key/rowid following insert, redux...
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Peter:

Trying to solve my problem mentioned in the email of half an hour ago, I searched
through the archives of the interface list and found some of your replies suggesting
using "currval()" to get the last value assigned from a sequence...  However,
here's what happens in a good database with multiple in-use sequences:

db=# select currval('foo_foo_id_seq');
ERROR:  foo_foo_id_seq.currval is not yet defined in this session

As an alternative, I discovered that I can get the value this way:

db=# select last_value from foo_foo_id_seq;
last_value
---------
              27

My questions are, (1) why does the currval() approach give the error message, and
(2) is it OK to use my alternative??

Finally, as far as I can tell, there is a real race condition problem here in a multiple-connection
scenario (e.g. another task can cause the sequence to be incremented between the insert
and the select) - but wrapping a transaction around the insert and select should
take care of it... Thoughts??

Thanks,
Mark Dzmura


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