Re: HOW 'VIEW' WORKS

Brian P. Mac Lean wrote:
>
> Alex Yau wrote:
> >
> > I have a question about exactly how VIEW works in ORACLE.
> >
> > I am working a bunch of reports which use a VIEW which is a UNION of
> > 2 hugh tables(150000 and 100000 rows respectively.) The report SQL
> > statement will use this view to join with other tables to select the
> > columns required.
> >
> > I would like to know how the SQL statement will be processed
> > internally? Will the VIEW be created first(i.e. full table scan,
> > sort/merge ...etc) THEN join with other tables OR the create
> > statement of the VIEW will be combined with the report SQL statement
> > first then process in one go.
> >
> > Thanks,
> >
> > Alex
>

The way I learned it ... although I may be getting confused with some other RDBMSs ...

the view statement is kept semi-parsed. The optimizer parses the requested statement. It then merges the view parse-tree and then optimizes - before the view is processed.

Alex' response about using Explain Plan should verify this.

/Hans Received on Mon Sep 30 1996 - 00:00:00 CEST