Re: LIMIT Optimization

Hi,

Syntax of the "optimization" in other plataforms:

DB2 : [Optimization For n Rows]  ( [Fetch-First n ] = PostgreSQL's LIMIT )
Oracle: [/*fastfirstrows*/]
SQL Server: [FastFirstRows] - version 6.x  // [FAST(n)] - version >= 2000

I simulate the "optmization" in PostgreSQL using:

1. SELECT * FROM <table> WHERE <cond> ORDER BY <order> LIMIT 10
(Explain this query show a Index Scan)

2. Loop in resultset. If the <cond> is break in <= 10 rows continue, else

3. Repeat the query without LIMIT

The times of queries in DB2 and PostgreSQL are same doing it.

------------

Alexandre


----- Original Message -----
From: "Tom Lane" <tgl@sss.pgh.pa.us>
To: "Bruce Momjian" <pgman@candle.pha.pa.us>
Cc: "alexandre paes :: aldeia digital" <alepaes@aldeiadigital.com.br>;
<pgsql-sql@postgresql.org>
Sent: Friday, January 25, 2002 3:58 PM
Subject: Re: [SQL] LIMIT Optimization


> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > So, it is only valuable for cursors
>
> Right; I can see no rhyme or reason for attaching it to a plain SELECT,
> unless the system provides some way of stopping short of fetching all of
> a SELECT, which we don't.  A CURSOR would be the analogous thing in PG.
>
> regards, tom lane