Bob Hairgrove wrote:
> [...] What bothers me most is that there is no apparent
> formal distinction between this:
>
> OrderID|CustomerID|Item1 |Item2 |Item3 | Item4 (...)
> =================================================================
> 1|foo_123 | apples| pears| bananas| oranges
> 2|bar_123 | pears| bananas| oranges|
> 3|bar_123 | bananas| | |
>
> etc., and this:
>
> OrderID|CustomerID|Items
> ================================================
> 1|foo_123 | apples;pears;bananas;oranges
> 2|bar_123 | pears;bananas;oranges
> 3|bar_123 | bananas
Actually there is a formal difference, because the first table has
redundancy. If you know that Item2 is empty, then you also know that
Item3 is empty, et cetera. Since normalization is about removing
redundancy and preventing update anomalies, the first table should be
considered as unnormalized. The second table does not have this problem.
Received on Wed Mar 01 2006 - 14:07:40 CST
