Re: primary keys

Randy A. Stebbins wrote:
<snip>
> I don't think you want a sequence. Sequences are for using ordered lists

Whoa, there. I believe the most common use of sequences is to generate a unique number (if you don't allow wrapping) to be used as a key or part of a key. It is perfectly valid to use something like this as a primary key in two circumstances:

1. To improve performance in cases where the real primary keys are numerous columns and/or large in size. This is really a denormalization.
2. In cases where the attributes CAN'T uniquely identify a row. Take ORDER, for example. I can enter two orders for the same stuff for the same customer at exactly the same second, so all the 'natural' data is identical. So you add order_number as the primary key. This works because the process decides when to create a new order, and it's not simply derived from the data itself. This really should be done in the design phase at a logical level and would not be just a denormalization.

> of numbers. A primary key is not something separate from a table. It is
> one (or more) columns of the table itself. When you identify a primary key
> for a table, Oracle creates an index on the key, and prevents any duplicate
> entries.
>

<snip>

-- 
Allen Kirby			AT&T ITS Production Services
akirby_at_att.com			Alpharetta, GA.