Written by SQLuser
Wednesday, 19 May 2010 03:16
Oracle
Normalization is the process of efficiently organizing data by eliminating redundant data and maintaining dependencies.
Summary: First Normal Form
* A relation is in 1NF if it contains no repeating groups
* To convert an unnormalised relation to 1NF either:
* Flatten the table and change the primary key, or
* Decompose the relation into smaller relations, one for the repeating groups and one for the non-repeating groups.
* Remember to put the primary key from the original relation into both new relations.
* This option is liable to give the best results.
Summary: Second Normal Form
* A relation is in 2NF if it contains no repeating groups and no partial key functional dependencies
* Rule: A relation in 1NF with a single key field must be in 2NF
* To convert a relation with partial functional dependencies to 2NF. create a set of new relations:
* One relation for the attributes that are fully dependent upon the key.
* One relation for each part of the key that has partially dependent attributes
Summary: Third Normal Form
* A relation is in 3NF if it contains no repeating groups, no partial functional dependencies, and no transitive functional dependencies
* To convert a relation with transitive functional dependencies to 3NF, remove the attributes involved in the transitive dependency and put them in a new relation
* Rule: A relation in 2NF with only one non-key attribute must be in 3NF
* In a normalised relation a non-key field must provide a fact about the key, the whole key and nothing but the key.
* Relations in 3NF are sufficient for most practical database design problems. However, 3NF does not guarantee that all anomalies have been removed.
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