Re: SQL join methods

From: Tommy Wareing <p0070621_at_brookes.ac.uk>
Date: Fri, 16 Oct 1998 10:55:12 GMT
Message-ID: <36272461.244560329@news.brookes.ac.uk>

On Thu, 15 Oct 1998 20:27:12 GMT, cn338_at_torfree.net (Kevin Macdonald) wrote:

>How many ways can SQL express a join relationship between two or
>more tables?

Hmmm... 2*number of possible function calls. So infinite :-)

simplest is "="
also "<" (which covers "between")
should "in (subquery)" be counted? I don't think "in (field1, field2)" counts, because that's identical to "=field1 or =field2"

Once you start including functions, you can write substr(field1, 1, 3)=substr(field2, 1, 3) and so forth, which therefore covers LIKE (the optimiser handles it differently, I know, but logically it's the same).

And anyway, once you've got up to 2*infinity, then I don't think it's worth arguing whether it should be 2, or 4!

--
Tommy Wareing
MIS Group
Learning Resources
Oxford Brookes University
01865 483389 Received on Fri Oct 16 1998 - 05:55:12 CDT