earthlink wrote:
>
> Frequently one wants a data set returned in the same order as the
> index used in the query. Informix (at least) has implicit order-by,
> which means that the data will be returned in collating order if the
> query forces use of the appropriate index.
>
> Does Postgresql do this?
If data is fetched by walking an index, then , yes it produces an
implicit order. Just don't count on it to stay that way - the use of a
particular index depends on too many things.
> If not, does an Order-by force a sort even if an index has the correct
> order to satisfy the order-by?
Dropping unneeded sort node from a query tree was one of the earliest
optimisations in postgresql.
---------------
Hannu
