From: "Qingqing Zhou" <zhouqq@cs.toronto.edu>
Subject: Re: Use of * affect the performance
Date: Mon, 16 Jan 2006 16:55:11 -0500
Organization: Hub.Org Networking Services
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Message-ID: <dqh4lf$2o66$1@news.hub.org>
References: <1137422968.1085.25.camel@servidor>
To: pgsql-performance@postgresql.org


"Marcos" <mjs_ops@gmx.net> wrote
>
> I always think that use of * in SELECT affected in the performance,
> becoming the search slowest.
>
> But I read in the a Postgres book's that it increases the speed of
> search.
>
> And now???? What the more fast?
>

If you mean use "*" vs. "explicitely name all columns of a relation", then 
there is almost no difference except the negligible difference in parsing. 
If you mean you just want part of the columns of a relation but you still 
use "*": Yes, you will save one projection operation for each result row but 
you will pay for more network traffic. In the worst case, say your "*" 
involves some toast attributes, you just hurt performance. Considering the 
benefits is so marginal and dangerous, I suggest stay with the idea that 
"only retrive the columns that you are interested in".

Regards,
Qingqing