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Re: A technical question about VIEWS

From: Cisco <prsingh_at_cisco.com>
Date: 1997/03/28
Message-ID: <01bc3bd0$bc9d6800$e0d044ab@prsingh-pc.cisco.com>#1/1

Hi

Any query condition is merged with view definition to create the output.

Oracle in one of the documents explains it with examples.

An example can be table a and b
with view ab as follows

create view ab as (select * from a,b where a.a = b.b); and you have a condition on for column c in table a like a.c = 10

select * from ab where ab.c = 10;

While executing this query oracle will execute

select * from a, b
where a.a = b.b
and a.c = 10;

The above is true in all the cases except for when view is created by group by clause.

Pratap

NNOOR <Nnoor_at_cris.com> wrote in article
<5hco8f$f85_at_chronicle.concentric.net>...
>
> I know what views are. I want to know how views handle queries which
> run against them. Is the view first built and then user's query is
> satisfied from the result set (ofcourse, when NOT running SELECT *), or
> the view is built only for the records which also satisfy user's
> query--i.e. dynamically changing it's query. Following example will
> explain the question I am trying to ask...
>
> Lets say a view is built by joining x tables. And if the Select * is
> run for the view then, say, it returns 10,000 rows. Now if a query is
> run against the view with a selection criteria which will result in, say,
> only 10 rows. How will Oracle handle this situation. Will it first create
> the view with 10,000 rows and then run the user's query on the result
> set or it will dynamically add the selection criteria to the view's
> query so that a result set with only 10 records is built?
>
> I am trying to establish that how "expensive" the view operation is
> for internal application development purposes...
>
> Thanks very much for your help!
>
> Regards,
> Nasir (nnoor_at_cris.com)
>
  Received on Fri Mar 28 1997 - 00:00:00 CST

Original text of this message

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