Re: more algebra

paul c wrote:
> I was trying to lookup some old posts, maybe started by Marshall, not
> sure about that, to do with defining keys. Finally gave up, for some
> reason the google new archive isn't my cup of tea.
>
>
> I remember thinking that keys could be defined algebraically something
> like this: Let {K} stand for the set of attributes of r that make a key,
>
> ( r GROUP ( {K} AS k ) ) {k} = ( r {K}) GROUP ( {K} AS k)) {k}
>
> will be true when r satisfies the key constraint.
>
> ( r GROUP ( {K} AS k ) ) {k} MINUS ( r {K}) GROUP ( {K} AS k)) {k}
>
> will contain rva's that include the keys of tuples that violate the
> constraint. UNGROUP could also be used.
>
>
> Seem to remember some objection or other, but not exactly what it was.
> ...

Oops, I can think of my own objections. Must have been thinking of something else because the above is definitely wrong. Received on Mon Apr 05 2010 - 02:18:03 CEST