Re: Relational Divsion
Date: 1 Jun 2006 03:54:30 -0700
Relational division comes in several flavors -- Codd's, Todd's and Romley's are the major ones. Basically, you can do it as exact division or division with a remainder. Chris Date's version in his text book says that a division by an empty set returns all of the divisor; my version returns none of them (which is Date's preferred answer!). Romley's division classifies the relationship as "none match", "some match", "match exactly", and "match with a remainder", making it the best choice for reporting.
I cover them in detail in SQL FOR SMARTIES and give Standard SQL code. Received on Thu Jun 01 2006 - 12:54:30 CEST