Re: Few confusing things about first normal form
Date: Wed, 22 Oct 2008 21:23:24 +0100
Formally speaking any relation is *always* in 1NF by definition. A table (for instance in SQL) is said to be in 1NF if it accurately represents some relation, ie. it has: no duplicate rows; unique column names; no nulls; at least one key. SQL doesn't permit multiple values in a column or repeating goups of columns so those problems do not arise.
Informally, other notions are sometimes claimed to be associated with 1NF. It is sometimes said that a column value "must" be "atomic" or that a collection of attributes representing the same or similar things is a violation of 1NF. The problem is that these are highly subjective ideas which don't make much sense as hard and fast rules. It's best to consider these as design guidelines and nothing to do with a formal definition of 1NF proper, which is simply the definition of a relation.
If you expect to learn these concepts from miscellaneous web sites then you will come to grief. Get a decent text by a respected author such as: http://www.amazon.com/Introduction-Database-Systems-8th/dp/0321197844
-- David PortasReceived on Wed Oct 22 2008 - 22:23:24 CEST