Re: When are projections done?

From: John Hurley <johnbhurley_at_sbcglobal.net>
Date: Tue, 2 Mar 2010 06:07:10 -0800 (PST)
Message-ID: <e742c04d-5d34-4b77-8b3e-e4337554c6c5_at_d27g2000yqf.googlegroups.com>

On Mar 2, 6:10 am, jbdhl <jbirksd..._at_gmail.com> wrote:

snip

> Consider a table and a query referring to only a subset of the columns
> in that table. How early in the query evaluation is the projection
> carried out?
>
> Are the columns to be selected filtered out as early as in the very
> access method that reads the table rows from the buffer, or are the
> projection handled later, after the whole row has been fetched by the
> access method?
>
> Does it depend on the complexity of the query, how far down the three
> that the projection is handled out?
>
> Thanks!

Why does it matter?

Any specific release you are investigating?

Any specific problem query that you are trying to optimize? Received on Tue Mar 02 2010 - 08:07:10 CST