Re: Implicit order-by in Postgresql?

From: Hannu Krosing <hannu(at)tm(dot)ee>
To: earthlink <news(at)tinyvital(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Implicit order-by in Postgresql?
Date: 2001-06-12 17:50:06
Message-ID: 3B26564E.2F7D82CE@tm.ee
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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

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