Thread: transaction
Hello list. We are migrating from Informix to PSQL. In Informix we used to do: - BEGIN WORK - INSERT ROW - IF FAILED THEN UPDATE ROW - COMMIT WORK In PSQL this does not seem to work because after the first error (the insert) everything is omitted. Has someone found a solution for this (we have 1000's of this type). Henk Sanders
On Tue, Apr 20, 2004 at 21:14:48 +0200, "H.J. Sanders" <hjs@worldonline.nl> wrote: > > Hello list. > > We are migrating from Informix to PSQL. > > In Informix we used to do: > > - BEGIN WORK > > - INSERT ROW > > - IF FAILED THEN UPDATE ROW > > - COMMIT WORK > > > In PSQL this does not seem to work because after the first error (the > insert) > everything is omitted. > > Has someone found a solution for this (we have 1000's of this type). This question has come up a few times over the last year and there isn't a great answer. Locking the table is a simple solution, but can lead to problems because of contention.
On Tue, Apr 20, 2004 at 09:14:48PM +0200, H.J. Sanders wrote: > > - BEGIN WORK > > - INSERT ROW > > - IF FAILED THEN UPDATE ROW > > - COMMIT WORK You can do it the other way. Begin, update; if 0 rows are updated then insert. A -- Andrew Sullivan | ajs@crankycanuck.ca
On Wed, Apr 21, 2004 at 12:58:56 +0530, denis@coralindia.com wrote: > > The code looks like: > > update tempxitag set qty = qty + nqty where > ccod = cccod > GET DIAGNOSTICS nFound = ROW_COUNT; > If nFound = 0 then > insert into tempxitag( ccod, qty) > values (cccod, nqty ); > End if; You still can get errors if two transactions try to refer to the same nonexistant record at the same time. Postgres doesn't do predicate locking so the update won't lock the to be inserted row and both transactions may see the record as not existing and both try to do an insert. Updating, checking the count and then trying an insert if the count was 0 and retrying if the insert fails may be a better approach than locking the table. However, since this is an existing application it may be hard to make this complicated of a change. If there is flexibility in how the task gets done, switching to something based on sequences is probably the way to go.
Hi,
You can achieve this by:
1. Create a new table
2. Insert the data in this.
3. Write a trigger on this table
4. In trigger issue UPDATE and check whether it updated any records. If NO,
fire INSERT. ( here, i am updating first and inserting.. just reverse )
The code looks like:
update tempxitag set qty = qty + nqty where ccod = cccod GET DIAGNOSTICS nFound = ROW_COUNT;
If nFound = 0 then insert into tempxitag( ccod, qty) values (cccod, nqty ); End if;
HTH
Denis
----- Original Message -----
From: Bruno Wolff III <bruno@wolff.to>
To: H.J. Sanders <hjs@worldonline.nl>
Cc: <pgsql-sql@postgresql.org>
Sent: Wednesday, April 21, 2004 7:30 AM
Subject: Re: [SQL] transaction
> On Tue, Apr 20, 2004 at 21:14:48 +0200,
> "H.J. Sanders" <hjs@worldonline.nl> wrote:
> >
> > Hello list.
> >
> > We are migrating from Informix to PSQL.
> >
> > In Informix we used to do:
> >
> > - BEGIN WORK
> >
> > - INSERT ROW
> >
> > - IF FAILED THEN UPDATE ROW
> >
> > - COMMIT WORK
> >
> >
> > In PSQL this does not seem to work because after the first error (the
> > insert)
> > everything is omitted.
> >
> > Has someone found a solution for this (we have 1000's of this type).
>
> This question has come up a few times over the last year and there isn't
> a great answer. Locking the table is a simple solution, but can lead to
> problems because of contention.
>
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