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you are at >> normalization >>3rd normal form

3rd normal form

Relation (table) is at 3NF if :

• is at 2NF
• every attribute is functional dependent only from primary key, so there can't exist any transitive dependencies

Example

name	surname	birthplace	district
Emil	Zając	Pszczyna	pszczyński
Zofia	Zima	Pszczyna	pszczyński
Eulalia	Jańska	Szczebrzeszyn	zamojski

table `people` before normalization In the above table the district is only partially dependent on the primary key, which is the name and surname. District name is functional dependent on the column with the place of birth of the person. For this reason, the table is not in the third NF. It should be noted here that there is redundancy because of repeated names pszczyński district. This may be the cause of the anomalies, because one can change the place of birth, but forget to change the name of the district.

name	surname	birthplace
Emil	Zając	Pszczyna
Zofia	Zima	Pszczyna
Eulalia	Jańska	Szczebrzeszyn

table `people` after normalization int 3NF

town	district
Pszczyna	pszczyński
Szczebrzeszyn	zamojski

sub-relation `towns` after normalization Standardization of table `people` to 3NF is to create additional table `towns`, which there will be kept information about ditrict of each town. [ wróć na górę strony ]