Re: Dual table

From: Dave <x_at_x.com>
Date: Sun, 09 Jan 2005 21:21:25 GMT
Message-ID: <pfhEd.7154$GG1.592@text.news.blueyonder.co.uk>

"Dave" <x_at_x.com> wrote in message
news:o_gEd.7132$GG1.5615_at_text.news.blueyonder.co.uk...
>
> "Noons" <wizofoz2k_at_yahoo.com.au> wrote in message
> news:1105304323.113501.139440_at_c13g2000cwb.googlegroups.com...
>> Anurag Varma wrote:
>>>
>>> Before posting such questions you should read the link which OP
>> posted.
>>> Its a huge thread in asktom .. and Connor has explained his reasoning
>> behind the index and behind IOT.
>>
>> Ah yes, the famous "XDUAL" thread! Great stuff.
>>
>> What I'd like to know is who invented the
>> name "DUAL" for this table and why.
>> Does any1 know?
>>
>
> i saw it in an article on a very old oramag a while ago, by chuck rozwat I
> believe - I shall try and find it again
>

as promised

http://www.oracle.com/technology/oramag/oracle/02-jan/o12sendmail.html

I created the DUAL table as an underlying object in the Oracle Data Dictionary. It was never meant to be seen itself, but instead used inside a view that was expected to be queried. The idea was that you could do a JOIN to the DUAL table and create two rows in the result for every one row in your table. Then, by using GROUP BY, the resulting join could be summarized to show the amount of storage for the DATA extent and for the INDEX extent(s). The name, DUAL, seemed apt for the process of creating a pair of rows from just one.
Chuck Weiss, Oracle Received on Sun Jan 09 2005 - 15:21:25 CST