On Mon, May 19, 2008 at 12:21:20AM -0400, Gregory Stark wrote:
> "Zoltan Boszormenyi" <zb@cybertec.at> writes:
> > Also, it seems there are no infinite recursion detection:
> >
> > # with recursive x(level, parent, child) as (
> > select 1::integer, * from test_connect_by where parent is null
> > union all
> > select x.level + 1, base.* from test_connect_by as base, x where base.child
> > = x.child
> > ) select * from x;
> > ... it waits and waits and waits ...
>
> Well, psql might wait and wait but it's actually receiving rows. A
> cleverer client should be able to deal with infinite streams of
> records.
That would be a very good thing for libpq (and its descendants) to
have :)
> I think DB2 does produce a warning if there is no clause it can
> determine will bound the results. But that's not actually reliable.
I'd think not, as it's (in some sense) a Halting Problem.
> It's quite possible to have clauses which will limit the output but
> not in a way the database can determine. Consider for example a
> tree-traversal for a binary tree stored in a recursive table
> reference. The DBA might know that the data contains no loops but
> the database doesn't.
I seem to recall Oracle's implementation can do this traversal on
write operations, but maybe that's just their marketing.
Cheers,
David.
--
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