Re: atomic

paul c wrote:

> Bob Badour wrote:
>

>> paul c wrote:
>>
>>> paul c wrote:
>>> ...
>>>
>>>> if those make sense, by the D&D definition of "cartesian product", I 
>>>> think r1 |x| r2 would be empty and I presume so would I(r1 |x| r2).
>>>
>>> Sorry, let me take that back, I think I should have said 
>>> intersection, not cartesian product.
>>
>> The join is empty. The intersection is empty. If one renamed one of 
>> the "car" attributes to something else, the join would have 4 rows.

r1:

Name Car
----------- ------------
{bill} {car1,car2,car4}
{john,fred} {car3}

r2:

Car Colour

----------------  ---------
{car1,car3,car4}  {red}
{car2}            {green}

r1 join ( r2 rename Car as Vehicle ):

Name           Car                 Vehicle            Colour
-------------  ------------------  -----------------  ---------------
{bill}         {car1,car2,car4)    {car1,car3,car4}   {red}
{bill}         {car1,car2,car4)    {car2}             {green}
{john,fred}    {car3}              {car1,car3,car4}   {red}
{john,fred}    {car3}              {car2}             {green}