Re: View Questions

Hi,
 see my comments inline:

In article <809bj4$qgf$1_at_autumn.news.rcn.net>,   "Alan Shein" <alanshein_at_erols.com> wrote:
> Due to the data consistency model, views contain only the data that
was
> committed at the time of the instantiation of the view.
>

no. this applies only to the currently running query. (read - consistent view (or snapshot) of your data. not to be confused with the database-object view/snapshot)

> Ken Lee <Ken.Lee_at_its.monash.edu.au> wrote in message
> news:38276E09.6EB4D7D9_at_its.monash.edu.au...
> > Gudday,
> >
> > We are going to have a database containing quite a number of active
> > views, maybe 50+. This database would also have a high update
> > transaction rate. So I am hoping someone could help answer a couple
of
> > questions I have regarding views and Oracle 8.
> >
> > A view, when activated, creates a virtual table based on the view
> > definition. The virtual table is stored in the temporary table
space.
> >

No, a view (as in create view) is not more than a stored query associated with a name. every time you select from a view oracle re- writes your query and reads the underlying table(s).

> > While the virtual table is being built does the database take out
any
> > sort of lock restrictions to maintain data integrity? ie: How does
> > Oracle deal with updates to the base table(s) during view
activation?
> >
> > While the view is in use and the base table data is changed how
does the
> > database deal with the changes? ie: How does Oracle deal with
changes
> > base table(s) changes while view is in use?

this is not applicable, as you always go to the table.

there is one exception to that: materialised views (new in 8.1) they behave as you described. useful mostly for data warehouses where you have expensive queries and infrequent updates.

Karsten

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Before you buy. Received on Tue Nov 09 1999 - 10:02:16 CST