Re: more on delete from join
Date: Fri, 28 Aug 2009 16:33:58 GMT
>> I don't know if the plural 'disjunctions' is a typo'. Do you mean that >> the resulting value of R stands for "r1 OR r2, etc." is true?
> I don't seem to be getting through.
> AND is to INTERSECTION as OR is to UNION.
That's a stretch, it would be more accurate to say that <AND> is to relational intersection as <OR> is to relational union. If what you wrote is what most people think it might help explain why so many want to associate the result of a relational operation with the operations used for form the result, even though the form of the resulting set of tuples offers no way to record the operations that were used to produce it.
I think it is kind of phony for people to appeal at all to algebraic operations in this way when the strict use of algebra can use <OR> to produce a relation that is algebraically equal to one produced by <AND>. That's why I sometimes say a union is always a join, even though it does seem to wind people up. The expression used to form a view can be said to persist only if it is recorded as a constraint, which I would say it should be. Received on Fri Aug 28 2009 - 18:33:58 CEST