Date: Tue, 22 Jan 2008 08:36:37 +0100
From: "A. Kretschmer" <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: currval() within one statement
Message-ID: <20080122073637.GB21676@a-kretschmer.de>
References: <4795984E.7030904@bankir.ru>
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am  Tue, dem 22.01.2008, um 10:16:30 +0300 mailte silly_sad folgendes:
> Helo
> 
> is it expected that the currval() changes its value between calls within 
> one statement ?
> 
> Look the following call:
> 
> INSERT INTO ttt (a,b) SELECT currval('ttt_id_seq'), 'const' FROM ttt2;

This fails if you never call nextval() for this sequence within this
session.


> 
> Where the trigger before insert on ttt is defined and this trigger calls 
>  nextval('ttt_id_seq').

You don't need a TRIGGER. Just define your table with (a serial, ...)
and omit the column a if you INSERT a new row.


> I was surprised having different values of currval() in ttt.a

If you call nextval() befor the insert, then returns the currval(), for
instance, 5. If you call your insert with the TRIGGER like above, the
currval() returns this value 5, but your trigger fires and increase the
value.  And, maybe, an other process has increased the sequence also.

Conclusion, don't call nextval() within a TRIGGER, and insert either
nextval() for the column or omit this column.


Andreas
-- 
Andreas Kretschmer
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