Re: 4 the FAQ: Are Commercial DBMS Truly Relational?
From: Kenneth Downs <firstinit.lastname_at_lastnameplusfam.net>
Date: Sun, 10 Oct 2004 20:54:37 -0400
Message-ID: <dklckc.mla.ln_at_mercury.downsfam.net>
>>But what if I mistype the last name when entering the second row? Now I
>>have "John Smith" and "John Smyth", with all other columns identical. The
>>rows are unique but wrong. So then we add a unique constraint on SSN, but
>>to every constraint we add I have a user who is going to put in a typo and
>>give a unique but incorrect answer.
>>
>>What body of theory do we depend upon to deal with this next level of
>>error?
>>
>>Practical experience seems to be that the Employee_ID column is the
>>answer. By requiring that single unique column, I can eventually trace
>>anomalies in the payroll system back to the presence of two "John Smith"
>>rows that have
>>different IDs. Great! Having discovered this human error after the fact,
Date: Sun, 10 Oct 2004 20:54:37 -0400
Message-ID: <dklckc.mla.ln_at_mercury.downsfam.net>
> Kenneth Downs <firstinit.lastname_at_lastnameplusfam.net> wrote: > > [snip] >
>>But what if I mistype the last name when entering the second row? Now I
>>have "John Smith" and "John Smyth", with all other columns identical. The
>>rows are unique but wrong. So then we add a unique constraint on SSN, but
>>to every constraint we add I have a user who is going to put in a typo and
>>give a unique but incorrect answer.
>>
>>What body of theory do we depend upon to deal with this next level of
>>error?
>>
>>Practical experience seems to be that the Employee_ID column is the
>>answer. By requiring that single unique column, I can eventually trace
>>anomalies in the payroll system back to the presence of two "John Smith"
>>rows that have
>>different IDs. Great! Having discovered this human error after the fact,
> > That single, unique column is also a constrained (PK). What > happens when a key for that column is entered wrong? Why would it be > any different for another key for another unique column, say SSN? >
-- Kenneth Downs Use first initial plus last name at last name plus literal "fam.net" to email meReceived on Mon Oct 11 2004 - 02:54:37 CEST