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(at)sss(dot)pgh(dot)pa(dot)us>
To: "Bruce Momjian" <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: "alexandre paes :: aldeia digital" <alepaes(at)aldeiadigital(dot)com(dot)br>;
<pgsql-sql(at)postgresql(dot)org>
Sent: Friday, January 25, 2002 3:58 PM
Subject: Re: [SQL] LIMIT Optimization

> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)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