Re: MV Keys

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.

• Jan Hidders