Re: Curious SQL question

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 06 Jan 2007 15:22:14 GMT
Message-ID: <G8Pnh.41302$cz.607601@ursa-nb00s0.nbnet.nb.ca>

Walt wrote:

> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:3INnh.41260$cz.607000_at_ursa-nb00s0.nbnet.nb.ca...
> 

>>J M Davitt wrote:
>>
>>>Neo wrote:
>>>
>>>
>>>>>select distinct orders.customer_id, products.product_id
>>>>> from orders, products
>>>>>minus
>>>>>select distinct customer_id, product_id
>>>>> from products;
>>>>>
>>>>>The first select esablishes a "universe of discourse" for the query

> 
> by
> 


>>>>>joining every customer with every product.  The second select excludes

>>>>>products that a customer did buy.

>>>>

>>>>The above SQL makes the solution easy to understand (should the last

>>>>line of the SQL be orders instead of products). Assuming the following:

>>>>

>>>>set A = {shampoo, soap, bread, wine}

>>>>set B = {shampoo, soap, bread}

>>>>set C = {wine}

>>>>

>>>>What is the most appropriate name of the function that does the

>>>>following:

>>>>

>>>>C = f (A, B);

>>>>

>>>>Is it NAND, NOT INTERSECTION, NOT IN? And should the order of the

>>>>inputs (A, B) matter?

>>>
>>>Uh, isn't that 'A MINUS B' or, if you prefer, MINUS (A, B).
>>
>>What about XOR(A,B) ?

> 
> Read Marshall's response, concerning "symmetric difference".
> 
> XOR  is commutative.  MINUS is not.  Unless I'm misreading something.

Indeed. I apologize for playing with the cranks.

How about f(A,B) = Drinks(A) union Vehicles(B) ? Received on Sat Jan 06 2007 - 09:22:14 CST