Re: Description of _complex_view_merging

Christian Hartmann wrote:
>
> Hi,
>
> the Oracle-support told us explicity to set _complex_view_merging to
> false to improve the performance of our database after migration from
> 8i to 9i.
>
> Can someone give us a short description what exactly this paramter is
> reponsible for?
>
> Regards,
>
> Christian

I think this is covered in the manuals.

A complex statement is something like

SELECT FROM tab1 WHERE col1 IN
(SELECT col1 FROM tab2)

ie, it doesn't have a join clause

If _complex_view_merging is TRUE it could be transformed into something like

SELECT tabl.col
FROM tab1,tab2
WHERE tab1.col1 = tab2.col1

In theory there are more and more powerful join operations available to the optimizer where there is a join clause. Received on Fri Dec 12 2003 - 11:58:09 CST