RE: the idea of unique primary keys to be a solution that hasoutl ived its usefulness?

["DeLong, Eric" <EDeLong@xxxxxxxxxxxxxxx>]

Joep,

Yes, I'll agree that compound keys can indeed be considered primary keys.  I
misspoke; I was thinking of "identity columns" which are commonly used in
databases as primary key.  

The difference between the two designs, imo, is that the widespread use of
compound keys makes for inefficient joins between tables.  

Eric DeLong
Sally Beauty Company
MIS-Project Manager (BSG)
940-898-7863 or ext. 1863



-----Original Message-----
From: Joep Beckeringh [mailto:joep.beckeringh@xxxxxxxxxx]
Sent: Wednesday, November 19, 2003 2:47 AM
To: RPG programming on the AS400 / iSeries
Subject: Re: the idea of unique primary keys to be a solution that
hasoutl ived its usefulness?


----- Original Message -----
From: "DeLong, Eric" <EDeLong@xxxxxxxxxxxxxxx>
To: "'RPG programming on the AS400 / iSeries'" <rpg400-l@xxxxxxxxxxxx>
Sent: Monday, November 17, 2003 10:24 PM
Subject: RE: the idea of unique primary keys to be a solution that hasoutl
ived its usefulness?


> Unique primary keys are not what most of us use on the iSeries.  We use
> unique compound keys, where the combination of many factors (keys) work
> together to define a unique row.  Unique primary keys are a single field
> that describes a unique row.  These are commonly implemented as UUIDs, or
> possibly as auto-incrementing value for such things as order number and
> whatnot...

Who says so? Primary keys can be compound.

>From 'A Guide to the SQL Standard' (C.J. Date / Hugh Darwen):

In SQL, a candidate key definition takes the form
    { PRIMARY KEY | UNIQUE } ( column-commalist ).
For a given base table, at most one candidate key definition can specify
PRIMARY KEY.

Joep Beckeringh

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