Re: Referencing serial col's sequence for insert

Am a bit confused -which one comes first?

1) the 'data'||currval('id01_col1_seq') is parsed first : which means it
takes the current session's currval
2) then the insert is attempted which causes a sequence.nextval to be
performed which means that 'data'||currval('id01_col1_seq')will be
different from the sequence's value

or

1) an insert is attempted which causes a sequence.nextval to be performed
and then
2) the cols are parsed for the insert so the 'data'||currval('id01_col1_seq')
has the correct value

I observe the latter on my single session notebook instance of postgres.

Regards,
AK

On Tue, Jul 22, 2014 at 10:53 PM, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>
wrote:

> David G Johnston wrote:
> >> Also, I think that your method is vulnerable to race conditions:
> >> If somebody else increments the sequence between the INSERT and
> >> "SELECT lastval()" you'd get a wrong value.
> >
> > Uh, no. It returns that last value issued in the same session - which is
> > race-proof.
> >
> > http://www.postgresql.org/docs/9.3/static/functions-sequence.html
> >
> > Both of them are useful and in the case of inserting multiple rows you
> have
> > to use RETURNING. Beyond though it is largely personal preference and
> > ease-of-use (dealing with a set when you know a single value is all that
> is
> > necessary can be annoying).
>
> You are right, I mixed it up with "currval".
>
> Yours,
> Laurenz Albe
>
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