Re: Normalization, Natural Keys, Surrogate Keys
Date: Tue, 28 May 2002 17:45:15 +0100
In message <2cf20de8.0205260901.19582f0a_at_posting.google.com >, Costin Cozianu <c_cozianu_at_hotmail.com> writes
>For example, in the above, because you allow for that 999999999 for
>situations that are very rare (let's say <1% or <5% of the cases), you
>fail to protect the vast majority of cases, because you won't be able
>to declarer the UNIQUE constraint on the SSN. There are better way to
>deal with this, one example that I suggested is create an
>SSN_Exceptions table where you put the data collected for the persons
>who don't have a SSN or their SSN has problems.
There's an alternative solution, add an extra integer field to the main
table with a default value of 0. Make the SSN and the new field a
composite key. When you have an unknown or invalid (or duplicate) SSN
insert a sequential number into the integer field. Any record with a
non-zero value should be considered an ongoing problem.
If you want you can create a view onto that table that will perform the
If you want you can create a view onto that table that will perform thesame functions as the SSN_Exceptions table.
-- Bernard Peek bap_at_shrdlu.com In search of cognoscentiReceived on Tue May 28 2002 - 18:45:15 CEST