Re: When are projections done?

From: John Hurley <>
Date: Tue, 2 Mar 2010 06:07:10 -0800 (PST)
Message-ID: <>

On Mar 2, 6:10 am, jbdhl <> wrote:


> 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

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