Re: Sequence

Alan, Simon,

You can't do this, at least not safely.

Sequences can't be rolled back and are visible across transactions. In
other words if thread 1 inserted a row, and before you read the sequence
thread b inserted a row, you would get the same value for both threads.
The only way I know is to get the sequence before hand and insert it.
The overhead is the same.

Dave

On Sat, 2003-01-11 at 20:19, Simon Mitchell wrote:
> Alan,
>             Just doing some test from psql prompt.
>
> After your insert into the table the id sequence is available by
>
> select currval('table_id_seq');
>  currval
> ---------
>     5006
> (1 row)
>
>
> If your session has not done an insert you should get an error.
> select currval('table_id_seq');
> ERROR:  table_id_seq.currval is not yet defined in this session
>
> Do a describe (\d) on your table to check seq name.
>
> So this is equivalent to MySql   >   last_insert_id() .
>
> ***************************************************
> If you wont the last value of the sequence (which could be your current
> session or another session) you can select it with
>
> SELECT last_value FROM  table_id_seq;
>  last_value
> ------------
>        5006
> (1 row)
>
> **This is not transaction safe as another session could have done an
> insert. Please use select currval('table_id_seq');**
> It is just nice to know.
> ***************************************************
>
> Simon
>
>
>
>
>
>
> Dave Cramer wrote:
>
> >Alan,
> >
> >You can't, get the sequence before and insert it.
> >
> >Dave
> >On Thu, 2003-01-09 at 14:35, Alan Roberto Romaniuc wrote:
> >
> >
> >>I have a table with sequence field (id).
> >>
> >>I insert a new row in this table, and I would like to get the sequence
> >>number that postgresql assign to id.
> >>
> >>How can I get it???  ... Max function is not nice.......
> >>
> >>jdbc2 ....
> >>
> >>
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>
>
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--
Dave Cramer <Dave@micro-automation.net>