Re: Are there terms for these?

From: Kenneth Downs <knode.wants.this_at_see.sigblock>
Date: Thu, 25 Aug 2005 00:09:30 -0400
Message-Id: <3rsvt2-lve.ln1@pluto.downsfam.net>

Marshall Spight wrote:

> Kenneth Downs wrote:

>> Given two tables that are not UNION compatible, it seems there are ways
>> to UNION them anyway.
>>
>> Method 1, Intersect their headers.  The resulting header is used to
>> project
>> both tables and now those projections are union compatible.  What would
>> this be called?

>
> We've been discussing this a lot. There was even a thead I started
> about
> a month ago called (IIRC) What would this operator be called?

This is scary, how did I miss it?

>
> Since then, I've been going with "inner union" or "generalized union".

What's weird is that normally somebody jumps in and points out that these ideas were first worked out in Sanskrit thousands of years ago and we should RTFM. How can it be that no terms exist and you are making them just now?

>
>

>> I suppose if the intersected headers yield an empty set
>> nothing would happen here.

>
> No! The empty-header-intersection case is *not* a special case;
> it's handled according to the uniform definition. It will have
> 0 attributes, and rows=0 if both operands are empty; rows=1 otherwise.
>
>
>

>> Method 2, Union their headers.  The resulting header is used to UNION
>> both tables, providing NULL or empty values where a column exists in one
>> but not
>> the other.  What would this be called, a FULL OUTER UNION (ha ha)?

>
> I'm calling it "outer union."
>

I suppose there really would be a LEFT OUTER UNION and a RIGHT OUTER UNION, though. Left would be all columns from table 1 plus common columns 1 and 2, or:

(L n R) U L (that 'n' is supposed to be intersection)

and RIGHT OUTER UNION would be all columns from right plus common columns, or:

(L n R) U L

-- 
Kenneth Downs
Secure Data Software, Inc.
(Ken)nneth@(Sec)ure(Dat)a(.com)

Received on Wed Aug 24 2005 - 23:09:30 CDT