From: Eric Lee on
On Sat, Feb 13, 2010 at 7:41 PM, Jochem Maas <jochem(a)iamjochem.com> wrote:

> Op 2/13/10 11:36 AM, Eric Lee schreef:
> >
> >
> > On Sat, Feb 13, 2010 at 6:55 PM, Jochem Maas <jochem(a)iamjochem.com
> > <mailto:jochem(a)iamjochem.com>> wrote:
> >
> > Op 2/13/10 10:08 AM, Lester Caine schreef:
> > > Rene Veerman wrote:
> > >> Hi.
> > >>
> > >> I'm looking for the most efficient way to insert several records
> and
> > >> retrieve the auto_increment values for the inserted rows, while
> > >> avoiding crippling concurrency problems caused by multiple php
> > threads
> > >> doing this on the same table at potentially the same time.
> > >
> > >> Any clues are greatly appreciated..
> > >> I'm looking for the most sql server independent way to do this.
> > >
> > > Rene
> > > The 'correct' way of doing this is to use a 'sequence' which is
> > > something introduced in newer versions of the SQL standard.
> > > Firebird(Interbase) has had 'generators' since the early days (20+
> > > years) and these provide a unique number which can then be
> > inserted into
> > > the table.
> > >
> > > ADOdb emulates sequences in MySQL by creating a separate table for
> the
> > > insert value, so you can get the next value and work with it,
> without
> > > any worries. The only 'problem' is in situations were an insert is
> > > rolled back, a number is lost, but that is ACTUALLY the correct
> > result,
> > > since there is no way of knowing that a previous insert WILL
> > commit when
> > > several people are adding records in parallel.
> >
> > this is all true and correct ...
> >
> > but that doesn't answer the problem. how do you get the IDs of all
> > the records
> > that we're actually inserted in a multi-insert statement, even if
> > you generate the
> > IDs beforehand you have to check them to see if any one of the set
> > INSERT VALUEs failed.
> >
> > @Rene:
> >
> > I don't think there is a really simple way of doing this in a RDBMS
> > agnostic
> > way, each RDBMS has it's own implementation - although many are
> > alike ... and MySQL is
> > pretty much the odd one out in that respect.
> >
> > it might require a reevaluation of the problem, to either determine
> > that inserting
> > several records at once is not actually important in terms of
> > performance (this would depend
> > on how critical the speed is to you and exactly how many records
> > you're likely to be inserting
> > in a given run) and whether you can rework the logic to do away with
> > the requirement to
> > get at the id's of the newly inserted records ... possibly by
> > indentifying a unique
> > indentifier in the data that you already have.
> >
> > one way to get round the issue might be to use a generated GUID and
> > have an extra field which
> > you populate with that value for all records inserted with a single
> > query, as such it could
> > function as kind of transaction indentifier which you could use to
> > retrieve the newly
> > inserted id's with one extra query:
> >
> > $sql = "SELECT id FROM foo WHERE insert_id = '{$insertGUID}'";
> >
> > ... just an idea.
> >
> > >
> >
> >
> >
> > Hi
> >
> > I would like to learn more correct way from both of you.
> > May I ask what is a sequences ?
>
> it an RDBMS feature that offers a race-condition free method of
> retrieving a new unique identifier for a record you wish to enter,
> the firebird RDBMS that Lester mentions refers to this as 'generators'.
>
> to learn more I would suggest STW:
>
> http://lmgtfy.com/?q=sql+sequence
>
>
Jochem


Thanks,

Regards,
Eric

> >
> >
> > Thanks !
> >
> >
> > Regards,
> > Eric
> >
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