Training and More

Andrew Coates MSFT Training and More | Quick Diets

Andrew Coates MSFT Training and More | Quick Diets — Wed, 10 Jun 2009 06:34:05 GMT

PingBack from http://quickdietsite.info/story.php?id=9342

Set-based Query Languages, Databases and Buses

notgartner.com: Mitch Denny's Blog — Tue, 05 Oct 2004 16:11:00 GMT

re: Training and More

Andrew Coates — Thu, 30 Sep 2004 06:42:00 GMT

Hi Nathan,

OK, I guess expressed that poorly. It's not the difference operator that's OO, but the concept of having data "objects" that we're taking the difference between. Date (mine is the 6th edition, but I guess this bit hasn't changed much) talks about the problem of type-compatibility (chapter 6 in my edition), and I guess that was what I was alluding to.

In relational algebra, relations involved in difference operations (and Union and Intersection) need to be type compatible (that is, the tuples in each set are the same type), but I'd see a case for having a difference operator, for example, that used a primary key from eack set to do the difference and then retained only the fields that were common to both sets.

re: Training and More

Nathan Allan — Wed, 29 Sep 2004 20:00:00 GMT

A difference operator is hardly an "object-oriented construct" and the idea of a relational difference operator has existed since Codd first laid the groundwork 35 years ago. Though not used by most SQL systems, there are systems that support such capabilities. For instance, the expression you have in your example would look like this in D4 (see Dataphor):

var MissingCustomers := ImportedCustomers - Customers;

For more information on difference and other relational operators, see "An Introduction to Database Management Systems 8th edition" by C. J. Date. This book should be in everyone's library.

Regards,

--
Nathan Allan