1NF: atomicity, that is, each field cannot be separated.
2NF: uniqueness, that is, each table describes only one entity. This entity must have a primary key. non-primary keywords must be fully dependent on the primary key because they are completely dependent, the reason is that in the case of a primary key combination, non-primary keywords cannot only rely on some keywords.
3NF: A table cannot contain the existing non-primary key fields in other tables. That is, it can only contain the primary key information of other tables. This is the primary key and foreign key, through the primary foreign key, you can join tables. 3NF is mainly used to reduce data redundancy.