数据库范化 database normalization

Database normalization is useful for several reasons:
        a. It helps to build a structure that is logical and easy to maintain.
        b. Normalized databases are the industry standard.
        c. Retrieving data will be easier.

First Normal Form means that the database doesn't contain any repeating attributes.
Violations of Second Normal Form occur when the table contains attributes that depend on a portion of the primary key.
Second Normal Form violations can exist only when you have a multi-column primary key.
Third Normal Form violations occur when a transitive dependency exists.
All attributes in entities (columns in tables) must be dependent upon the primary key or one of the candidate keys and not on other attributes.