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) ?
Received on Sat Jan 06 2007 - 07:43:27 CST
