Re: Does entity integrity imply entity identity?
Date: Sat, 01 Aug 2009 21:48:19 GMT
"Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> Mr. Scott wrote:
>> Since the entity integrity rule ensures that a relational table cannot
>> have any duplicate rows, does that imply that each row in a table maps to
>> a distinct entity?
> I am unfamiliar with an entity integrity rule. It sounds like some shit
> somone just made up to market ER diagrams.
I learned the entity integrity rule back in 1984, at the same time I learned
the referential integrity rule.
It didn't seem like shit then, and it doesn't seem like shit now.
The entity integrity rule just says a table's key data may not be null, and must be unique. In SQL, declaring a primary key is sufficient to enforce both the uniqueness rule and the not null rule. This rule was presented particularly for tables that represent entities. The concept is that each entity must have a unique key. Otherwise you can't keep entities distinct. Received on Sat Aug 01 2009 - 23:48:19 CEST