Re: Little design mistakes that can be easily avoided (2): Listenning to CELKO (and CELKO alikes)

"David Cressey" <cressey73_at_verizon.net> wrote:

>
>"Matthias Klaey" <mpky_at_hotmail.com> wrote in message
>news:5bsi53h8bt88nf7iaj0tpk6e3rbjkv9mh8_at_4ax.com...
>> Cimode <cimode_at_hotmail.com> wrote:
>>
>> >On 27 mai, 05:16, paul c <toledobythe..._at_oohay.ac> wrote:
>> >> Matthias Klaey wrote:
>> >> > Cimode <cim..._at_hotmail.com> wrote:
>> >> > ...
>> >>

[...]

>> 1. In the Relational Model, the key is part of the definition of a
>> relation (= table in practice). You don't have a relation if it
>> doesn't have a key.
>
>I differ with the wording above. Here's an alternate wording: if you have
>a relation, the tuples will be distinct, by definition. This means that the
>entire tuple is either a candidate key or a super key. To discover
>candidate keys, one merely needs to discover the constraints placed on the
>data.

Yes, thank you for the clarification.

[..]

>> 4. When you construct a dbms (and only then), you might want to
>> investigate surrogate keys, mostly for performance reasons.
>
>In my experience, performance has little to do with it.

I am not close enough to building a dbms, so I am probably mistaken about this.

Greetings
Matthias Kläy

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