Re: separate table or no
The set of columns b is functionally dependent on the set of columns a if there is no more than one value of b for any a. We say a determines b, or a→b. If the city is Toronto, the province is Ontario.
A table is in Boyce-Codd Normal Form (BCNF) if for every functional dependency, a→b is trivial since a is in b, or a is unique, ie a is a superkey. The city→province dependency meets the BCNF criterion if and only if every value of city is unique. If this uniqueness fails, then updates WHERE city='Stratford' will apply to cities of that name in Ontario, Quebec and Prince Edward Island---not likely the intention.
If you think about it, you could follow that logic down so many real-world dependency chains, your client finally gets tired of waiting and finds herself a less obsessive developer. So the question usually comes down to finding the point where the efficiency gains from normalisation are outweighed by their unimportance or rarity.
Subject
Written By
Posted
February 02, 2021 03:36AM
February 02, 2021 12:33PM
February 03, 2021 02:10AM
Re: separate table or no
February 03, 2021 11:35AM
Sorry, you can't reply to this topic. It has been closed.
Content reproduced on this site is the property of the respective copyright holders.
It is not reviewed in advance by Oracle and does not necessarily represent the opinion
of Oracle or any other party.