Re: When are projections done?

"jbdhl" <jbirksdahl_at_gmail.com> wrote in message news:43971ed0-54f7-4094-84af-40eb1d00a946_at_f8g2000yqn.googlegroups.com...
>> At the earliest possible moment.
>
> Could that be directly inside the access method that fetches
> individual rows from the page in the buffer? Or is the projection
> always performed at some point *after* the initial fetch of the
> relevant row(s)?

If you wanted a definite answer you'd have to ask the Oracle programmers. But it wouldn't make sense to copy a row from a buffered block into local memory and then extract the fields from the local copy - so I think you can assume that the copy from the buffered block extracts only the columns needed from the row. (There are aspects of the CPU costing algorithm that tend to confirm this,)

-- 
Regards

Jonathan Lewis
http://jonathanlewis.wordpress.com