Article From:https://www.cnblogs.com/deltadeblog/p/9689679.html

 

normal formIt can be understood as the criteria and rules for designing data tables.

 

First paradigm

One paradigm is the indivisibility of attributes. Property is the field in the table as well as the column in the table. Indivisible is that the property is the smallest unit and can no longer be divided into smaller units.

For example, the student information table has the attributes of school number, name, gender and so on. The student number, name and gender are inseparable, so it meets the requirements of the first paradigm.

If the student schedule contains the property of curriculum, and the curriculum contains (mathematics, English, etc.), then the property of curriculum does not conform to the first paradigm and should be further divided.

 

Second paradigm

To satisfy the first paradigm, a table must have a primary key, and columns that are not included in the primary key must depend entirely on the primary key, not only on a part of the primary key. The second paradigm requires that every instance or row of a data table must be uniquely identified, and the uniquely identified must depend on the primary key.

 

 

Third paradigm

Satisfies the second paradigm, each non-primary attribute cannot be passed dependent on the primary key, and each non-primary attribute must be directly dependent on the primary key.

For example, the student information table has the attributes of school number, name, gender, school address, school contact mode and so on, where the school number is the main key, name, gender and school directly depends on the school number, but the school address and school contact mode is directly dependent on the school, indirectly depends on the primary key school number, so it does not conform to the third paradigm.

 

 

More explanation: https://www.zhihu.com/question/24696366

 

Link of this Article: Relational database three paradigm

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