The goal of the first normal form is to ensure the atomicity of each column.
This question examines the understanding of the three major paradigms of the database. The answers to this question abc are correct, and the answer to d must be designed in accordance with the three paradigms. Sometimes there is a certain contradiction between design standardization and performance. In standardized design On the basis, allow certain redundant columns to appear
The second normal form requires each table to describe one thing
Database design steps, database design steps include collecting information, identifying entities, identifying relationships between entities, and identifying relationships between entity attributes
First normal form: When all the attributes of the relational model R cannot be decomposed into more basic data units, it is said that R satisfies the first normal form, abbreviated as 1NF. Satisfying the first normal form is the minimum requirement for the standardization of the relational model. Otherwise, there will be many basic operations that cannot be realized in such a relational model.
Second normal form: If the relational model R satisfies the first normal form, and all non-primary attributes of R are completely dependent on each candidate key attribute of R, it is said that R satisfies the second normal form, abbreviated as 2NF.
Third normal form: Let R be a relational model that satisfies the conditions of the first normal form, and X is any attribute set of R. If X is non-transitively dependent on any candidate keyword of R, then R is said to meet the third normal form, which is abbreviated as 3NF .