Thread: Re: [GENERAL] Bug with sequence
It seems worth pointing out, too, that some SQL purists propose not
relying on product-specific methods of auto-incrementing.
I.e., it is possible to do something like:
insert into foo( col, ... )
values( coalesce( ( select max( col ) from foo ), 0 ) + 1, ... );
and this is easily placed in a trigger.
-tfo
In article <7017.1037851915@sss.pgh.pa.us>,tgl@sss.pgh.pa.us (Tom Lane) wrote:
> Justin Clift <justin@postgresql.org> writes:
> > Oliver Elphick wrote:
> >> I created a sequence using SERIAL when I created a table. I used the
> >> same sequence for another table by setting a column default to
> >> nextval(sequence).
> >>
> >> I deleted the first table. The sequence was deleted too, leaving the
> >> default of the second table referring to a non-existent sequence.
>
> > This sounds like a serious bug in our behaviour, and not something we'd
> > like to release.
>
> We will be releasing it whether we like it or not, because
> nextval('foo') doesn't expose any visible dependency on sequence foo.
>
> (If you think it should, how about nextval('fo' || 'o')? If you think
> that's improbable, consider nextval('table' || '_' || 'col' || '_seq').)
>
> The long-term answer is to do what Rod alluded to: support the
> Oracle-style syntax foo.nextval, so that the sequence reference is
> honestly part of the parsetree and not buried inside a string
> expression.
>
> In the meantime, I consider that Oliver was misusing the SERIAL
> feature. If you want multiple tables fed by the same sequence object,
> you should create the sequence as a separate object and then create
> the tables using explicit "DEFAULT nextval('foo')" clauses. Doing what
> he did amounts to sticking his fingers under the hood of the SERIAL
> implementation; if he gets his fingers burnt, it's his problem.
>
> > Specifically in relation to people's existing scripts, and also to
> > people who are doing dump/restore of specific tables (it'll kill the
> > sequences that other tables depend on too!)
>
> 7.3 breaks no existing schemas, because older schemas will be dumped
> as separate CREATE SEQUENCE and CREATE TABLE ... DEFAULT nextval()
> commands.
>
> regards, tom lane
Of course, those would be SQL purists who _don't_ understand
concurrency issues. ;-)
---------------------------------------------------------------------------
Thomas O'Connell wrote:
> It seems worth pointing out, too, that some SQL purists propose not
> relying on product-specific methods of auto-incrementing.
>
> I.e., it is possible to do something like:
>
> insert into foo( col, ... )
> values( coalesce( ( select max( col ) from foo ), 0 ) + 1, ... );
>
> and this is easily placed in a trigger.
>
> -tfo
>
> In article <7017.1037851915@sss.pgh.pa.us>,
> tgl@sss.pgh.pa.us (Tom Lane) wrote:
>
> > Justin Clift <justin@postgresql.org> writes:
> > > Oliver Elphick wrote:
> > >> I created a sequence using SERIAL when I created a table. I used the
> > >> same sequence for another table by setting a column default to
> > >> nextval(sequence).
> > >>
> > >> I deleted the first table. The sequence was deleted too, leaving the
> > >> default of the second table referring to a non-existent sequence.
> >
> > > This sounds like a serious bug in our behaviour, and not something we'd
> > > like to release.
> >
> > We will be releasing it whether we like it or not, because
> > nextval('foo') doesn't expose any visible dependency on sequence foo.
> >
> > (If you think it should, how about nextval('fo' || 'o')? If you think
> > that's improbable, consider nextval('table' || '_' || 'col' || '_seq').)
> >
> > The long-term answer is to do what Rod alluded to: support the
> > Oracle-style syntax foo.nextval, so that the sequence reference is
> > honestly part of the parsetree and not buried inside a string
> > expression.
> >
> > In the meantime, I consider that Oliver was misusing the SERIAL
> > feature. If you want multiple tables fed by the same sequence object,
> > you should create the sequence as a separate object and then create
> > the tables using explicit "DEFAULT nextval('foo')" clauses. Doing what
> > he did amounts to sticking his fingers under the hood of the SERIAL
> > implementation; if he gets his fingers burnt, it's his problem.
> >
> > > Specifically in relation to people's existing scripts, and also to
> > > people who are doing dump/restore of specific tables (it'll kill the
> > > sequences that other tables depend on too!)
> >
> > 7.3 breaks no existing schemas, because older schemas will be dumped
> > as separate CREATE SEQUENCE and CREATE TABLE ... DEFAULT nextval()
> > commands.
> >
> > regards, tom lane
>
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-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square,
Pennsylvania19073
"Thomas O'Connell" <tfo@monsterlabs.com> writes:
> It seems worth pointing out, too, that some SQL purists propose not
> relying on product-specific methods of auto-incrementing.
> I.e., it is possible to do something like:
> insert into foo( col, ... )
> values( coalesce( ( select max( col ) from foo ), 0 ) + 1, ... );
> and this is easily placed in a trigger.
... but that approach is entirely unworkable if you want any concurrency
of insert operations. (Triggers are a tad product-specific, too :-()
regards, tom lane
On Thu, 2002-11-21 at 14:11, Bruce Momjian wrote: > Of course, those would be SQL purists who _don't_ understand > concurrency issues. ;-) Or they're the kind that locks the entire table for any given insert. -- Rod Taylor <rbt@rbt.ca>
On 21 Nov 2002, Rod Taylor wrote: > On Thu, 2002-11-21 at 14:11, Bruce Momjian wrote: > > Of course, those would be SQL purists who _don't_ understand > > concurrency issues. ;-) > > Or they're the kind that locks the entire table for any given insert. Isn't that what Bruce just said? ;^)