Re: tricky query

> On Tue, Jun 28, 2005 at 12:02:09 -0400,
> Merlin Moncure <merlin(dot)moncure(at)rcsonline(dot)com> wrote:
> >
> > Confirmed. Hats off to you, the above some really wicked querying.
> > IIRC I posted the same question several months ago with no response
and
> > had given up on it. I think your solution (smallest X1 not in X) is
a
> > good candidate for general bits, so I'm passing this to varlena for
> > review :)
> >
> > SELECT t1.id+1 as id_new FROM id_test t1
> > WHERE NOT EXISTS
> > (SELECT t2.id FROM id_test t2 WHERE t2.id = t1.id+1)
> > ORDER BY t1.id LIMIT 1;
>
> You need to rework this to check to see if row '1' is missing. The
> above returns the start of the first gap after the first row that
> isn't missing.

Correct.

In fact, I left out a detail in my original request in that I had a
starting value (easily supplied with where clause)...so what I was
really looking for was a query which started at a supplied value and
looped forwards looking for an empty slot. John's supplied query is a
drop in replacement for a plpgsql routine which does exactly this.

The main problem with the generate_series approach is that there is no
convenient way to determine a supplied upper bound. Also, in some
corner cases of my problem domain the performance was not good.

Merlin