Re: getting the last N tuples of a query

From: Ben Chobot <bench(at)silentmedia(dot)com>
To: Edmundo Robles L(dot) <erobles(at)sensacd(dot)com(dot)mx>
Cc: "pgsql-general" <pgsql-general(at)postgresql(dot)org>
Subject: Re: getting the last N tuples of a query
Date: 2010-07-08 23:32:52
Message-ID: 3508844C-6813-431F-9638-C3D96578962E@silentmedia.com
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On Jul 8, 2010, at 4:17 PM, Edmundo Robles L. wrote:

> Hi!
>
> if a want the first 5,10,N tuples of a query (even without order)
> i just have to do a:
> select * from table limit 10;

That does not get the first 10 tuples, it merely gets 10 tuples. The database is free to return whichever 10 it can, and in practice, the results will change given enough inserts or deletes.

> So, what is the right way to do that with no order????

Without an order by clause, there is no concept of "first" or "last". Once you have the order by clause, combine your limit with ascending or descending sorts to get the first or last, respectively.

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