Hi,
Bruce Momjian:
> >
> > test=# explain select id from bench1 order by id;
> > Sort (cost=38259.21..38259.21 rows=300000 width=4)
> > -> Seq Scan on bench1 (cost=0.00..6093.00 rows=300000 width=4)
> >
> The heap is unordered, meaning a sequential scan and order by is usually
> faster than an index walk unless there is a restrictive WHERE clause.
>
What heap? The index is a b-tree in this case. Thus you should be able
to walk it and get the sorted result without ever touching the data
file.
Whether that makes sense with the current structure of the PostgreSQL
backend is a different question, of course. Certain othr databases
(no, not just MySQL ;-) are capable of doing that optimization, however.
--
Matthias Urlichs | noris network GmbH | smurf@noris.de | ICQ: 20193661
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