Re: Are there terms for these?

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?

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

> 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."

Marshall Received on Thu Aug 25 2005 - 00:14:29 CEST