Three paradigms of database

One 、 Database paradigm

1. First normal form —— Atomicity
   Each attribute in the data table can no longer be divided into smaller attributes
   
   The above table , Commodities can also be divided into commodity name and quantity , This attribute does not conform to atomicity .
2. Second normal form
   Every non primary attribute function depends on any candidate code （ Main attribute ）
   A relationship is a piece of data in a data table
   
   Student number , The name can be used as the identification of any relationship in the table , But the name may repeat , Student No , So choose the student number as the main code .
   Candidate codes are attributes in a relationship that can identify the relationship （ Main attribute ： Student number , full name ）
   There are multiple candidate codes for the same relationship , You have to choose a main code
3. Third normal form
   Nonprimary attributes are neither code dependent nor transitive , It's not part of the code .（ Each non primary attribute is completely independent of any candidate code ）