Re: Can FK be nullable/optional by design?

From: Louis Davidson <>
Date: Wed, 17 Dec 2003 16:32:04 -0600
Message-ID: <eIq0Z2OxDHA.1484_at_TK2MSFTNGP09.phx.gbl>

"Tobes (Breath)" <> wrote in message news:brq3iu$5nfbc$

> Hmmm, I thought Data Types (including UDTs) did enforce business rules, by
> constraining the set of possible values that can be stored in a column
> constrained to that type. If a business rule dictates that data of a
> type must fall within a spefic range, for example, then by defining a type
> that imposes this constraint, the business rule could be enforced by the
> Data Type?

The type of data type chosen is the first step in enforcing business rules. Clearly if the business rule states this will be an integer between -100 and 100, then you first choose a datatype. In this case, you might go with a smallint, or just an integer. Then you apply a check constraint. A proper Domain or a User Defined Type will include the datatype and some of the checking needed. If you chose a varchar for instance, the user would be able to insert whatever into the column, unless you built more elaborate checking into your column.

Louis Davidson (
Compass Technology Management

Pro SQL Server 2000 Database Design

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Received on Wed Dec 17 2003 - 23:32:04 CET

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