Shulou(Shulou.com)06/01 Report--

The relations in relational database need certain requirements, and those satisfying different requirements are different paradigms.

The normal form is downward inclusive, i.e. the first normal form must be satisfied to satisfy the second normal form.

First Normal Form (1NF): The one that meets the most requirements is called the first normal form. The first normal form requires that all fields are meaningful, atomic, and indivisible. First and last names, for example, cannot be separated.

The second normal form (2NF) requires that each tuple (i.e., each row of records) in a database table must be uniquely distinguishable, i.e., the table must have a primary key or primary key.

The third normal form (3NF) requires that database tables do not contain non-primary keyword information already contained in other tables. For example, in the student table, only the class ID should be included, and the class name cannot be included, because the class table already has a class name that is not the primary keyword.

BCNF is the complementary normal form of the third normal form, the fourth normal form and the fifth normal form in database design.

In database design, try to satisfy the third normal form. Generally, the method of designing database is to extract corresponding tables and fields according to conceptual model, remove redundant fields and dependencies according to normal form requirements, and at least meet the requirements of the third normal form, but adjust the database table structure locally according to performance and development convenience, and make some redundant fields.

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