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Re: Implementing complicated constraints

From: Mark C. Stock <mcstockX_at_Xenquery>
Date: Wed, 29 Sep 2004 15:09:19 -0400
Message-ID: <BOWdnWxvSfwelcbcRVn-jA@comcast.com>

"Tony Andrews" <andrewst_at_onetel.com> wrote in message news:1096478497.987036.104820_at_k17g2000odb.googlegroups.com...
| Brian Dick wrote:
| > On 28 Sep 2004 08:11:44 -0700, Tony Andrews wrote:
| > > Of course, having the CID in the A table is a viable work-around,
| but
| > > that doesn't mean there was a relational design flaw before.
| >
| > You need to brush up on your normalization rules. Rule 3 states that
| > columns must be dependent on nothing but the key. Your ATXT column is
| not
| > solely dependent on AID, so your design is not normalized.
|
| Wrong. ATXT is solely dependent on AID, it cannot be determined from
| CID. But there is an additional constraint that ATXT must be unique
| w.r.t. the CID for some reason. If you still think I'm wrong, then
| please show the NORMALIZED database design that resolves the issue.
| Not that it was MY column or design anyway!
|

from one of my other posts:
<snip>
keep in mind that if these are dependent tables, the natural key structure would be:

C
CID
PK (CID ) B
CID
BID
FK(CID) ref C
PK(CID, BID) A
CID
BID
AID
TXT
FK(CID, BID) ref B
PK(CID, BID, AID)
</snip> Received on Wed Sep 29 2004 - 14:09:19 CDT

Original text of this message

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