Re: diff. between Primary-Key and unique index

>if a column is declared as a unique key it will allow null
>value in that column (but only once) since the column is unique and
>therefore null values can occur but only once

from my point of understanding 'null' is similar to infinity in mathematics. nothing can be equal to infty. for that very reason null IS null but (null=null) IS null..

so i don't understand how null can be really unique or why on the other hand, null isn't allowed in a pk (w/ the same semantics)

anybody any further insights?

ciao, jan

http://www.rsp.de - Software zur effizienten Erstellung und Verwaltung von Gutachten, Analysen, Pruefprotokollen etc. Received on Sat Jan 22 2000 - 04:53:07 CST