Re: Query inside transaction

OK, thanks Michal, I did not know this issue. I thought I should use LOCK table inside the transaction to pick up the correct id value from SELECT MAX(id) FROM e_catalog.

On 25/06/2004 12.38, Michal Táborský <michal(at)taborsky(dot)cz> wrote:
>NMB Webmaster wrote:
>
>> But if someone else runs the same transaction in the same time
>what
> > value does "currval('sequence')" return? That one of the first
> > transaction or that one of the other transaction? Moreover, field
> > id is a unique primary key, it does not accept duplicates.
>
>That's the beauty of sequences. They are transaction-safe. Co
>"currval('sequence')" will always return the same value of the previous
>
>nextval call within that transaction, no matter how many other
>transactions picked the numbers in between.
>
>To demonstrate:
>
>Transaction 1 Transaction 2
>BEGIN; --
>nextval('seq') = 1 BEGIN;
>do something.. nextval('seq') = 2
>do something else... COMMIT;
>currval('seq') = 1
>COMMIT;
>
>--
>Michal Taborsky
>http://www.taborsky.cz
>
>
>