Re: When are projections done?
From: The Boss <usenet_at_No.Spam.Please.invalid>
Date: Tue, 2 Mar 2010 22:24:02 +0100
Message-ID: <4b8d81f4$0$22390$e4fe514c_at_dreader31.news.xs4all.nl>
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!
Date: Tue, 2 Mar 2010 22:24:02 +0100
Message-ID: <4b8d81f4$0$22390$e4fe514c_at_dreader31.news.xs4all.nl>
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!
What problem are you trying to solve, given the fact that you've been asking
this very same question in groups/forums for 3 different DBMS's:
comp.databases.oracle.server
comp.databases.ibm-db2
http://www.eggheadcafe.com/software/aspnet/35820528/when-are-projections-done.aspx
(MSSQL-forum)
-- JeroenReceived on Tue Mar 02 2010 - 15:24:02 CST