About database standardization

First paradigm

Each field in the table must contain only one type of data, and each data must be stored in only one place.

Example of a violation of the first paradigm: a field contains two data, or duplicate fields.

Second paradigm

When a table already complies with the first paradigm, and each table contains data with only one entity.

During the operation, you only need to ensure that the primary keyword of each table can be identified, and all non-key fields depend on this primary keyword rather than other fields.

Tip: to implement the many-to-many relationship in SQL Server, you need to use an intermediate connection table to break down the relationship into two one-to-many relationships.

Third paradigm 

The database must conform to the second paradigm, and all non-Keyword fields must directly rely on the primary keyword.

The most obvious violation of the third paradigm is the calculation field.

Another way to consider the third paradigm is to make each table contain only one thing of information.