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Second normal form partial dependency removed - Database
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Q. Which normal form is the partial dependency removed?
- Published on 19 Oct 15
a.
First
b.
Second
c.
Third
d.
BCNF
ANSWER: Second
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Discussion
Nirja Shah
-Posted on 29 Oct 15
- A technique of organising data is known as database Normalisation.
- It is a systematic approach of decomposing tables to eliminate data redundancy and undesirable characteristics like Insertion, Update and Deletion Anamolies.
- There is a multi-step process followed that puts data into tabular form by removing duplicated data from the relation tables.
- It is mainly used for two purpose:
1. Eliminating the reduntant(useless) data.
2. Ensuring data dependencies make sense i.e data is logically stored.
1 NF
- In this form, no two Rows of data must contain repeating group of information i.e each set of column must have a unique value, such that multiple columns cannot be used to fetch the same row.
- Every table in the database should be organized into rows, and each row should have a primary key that distinguishes it as unique.
- The Primary key is usually a single column, but sometimes a combination of more than one column is used to create a single primary key.
2NF
- In this form there must not be any partial dependency of any column on primary key.
- It means that for a table that has concatenated primary key, each column in the table that is not part of the primary key must depend upon the entire concatenated key for its existence.
- A table fails Second normal form when any column depends only on one part of the concatenated key.
3NF
- This form applies that every non-prime attribute of table must be dependent on primary key, or we can say that, there should not be the case that a non-prime attribute is determined by another non-prime attribute.
- The transitive functional dependency should be removed from the table and also the table must be in Second Normal form.
BCNF
- This normal form is a higher version of the third normal form.
- It deals with certain type of anomaly that is not handled by 3NF.
- A 3NF table which does not have multiple overlapping candidate keys is said to be in BCNF.
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