Re: Side effect of replacing a table with a view
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Sun, 24 Apr 2005 10:03:12 +0100
Given the early versions of Oracle, there
are likely to be some queries where the
optimizer instantiates the view before
performing a join. The first example that
springs to mind is the outer join:
Try something like this:
select {cols}
from
driver_table d,
table_a a
where
a.primary_key(+) = d.colX
;
Then replace table_a with the view equivalent.
I think you'll find in the execution plan that
the path stops using the primary key on table_a
and switches to a full scan with VIEW instantiation
appearing as the parent operation.
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/seminar.html
Public Appearances - schedule updated April 5th 2005
On 4/22/05, Vlado Barun <vlado@xxxxxxxxxx> wrote:
>
> I'm looking for input on what possible negative side effects I could
> encounter, if I replace a table with a view.
>
> Situation:
>
> I need to add a few columns to an existing, non-partitioned, heap table
> (let's call it "a"). However, I have identified a large number of "select
> *
> " queries against this table. Finding where these queries are coming from
> and changing them is not feasible within the current environment.
>
> So, I'm basically looking at two alternatives:
>
> 1. rename the existing table to "b", add the new columns to it and
> create a view named "a". The view will not expose any of the new columns
> 2. create another table "a_ext", with the same PK as "a", enforce RI
> (cascade delete), add the new columns to it. Also add an update trigger on
> "a", in case the PK in "a" gets updated, so that the PK in "a_ext" gets
> updated too.
>
> I prefer #1, but I'm concerned about possible negative side effect of
> renaming the table. Let's not worry about downtime, since it's not an
> issue
> in this environment. However, since table "a" is a very critical table, we
> need to make sure we do not break any existing code.
>
> We use Oracle 8.1.7.0 <http://8.1.7.0>, and yes it is .0, not .4
>
> Question:
>
> Are there any operations that could fail as the result of replacing the
> table with a view?
>
> Vlado Barun, M.Sc.
>
> Senior Data Architect, Cadre5
>
> www.cadre5.com <http://www.cadre5.com> <http://www.cadre5.com/>
>
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