In addition to Weibo, there is also WeChat
Please pay attention
WeChat public account
Shulou
2025-04-05 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Database >
Share
Shulou(Shulou.com)06/01 Report--
1NF: each column of a database table is an indivisible basic data item.
Analysis: there are no multiple columns that represent the same property; the value of a column cannot be a collection. It is almost impossible to represent an one-to-many relationship as multiple attributes of a table or multiple values of an attribute.
Solution: create a new table with "1" as the foreign key of the new table.
For example:
Person
Id
Name
Hobby1
Hobby1
Bobby3
one
Mark
Playing football
Running
Swimming
Or
Person
Id
Name
Hobbies
one
Mark
Playing football,running,awimming
2NF: conforms to 1NF; there is a primary key and there are no partial functional dependencies (there are no columns that depend on part of the primary key)
Analysis: in the case of combined keys, some columns depend on only part of the combined primary key, then it does not conform to 2NF.
Solution: move the columns that involve some functional dependencies out of the old table and save them in the new table. Or use artificial primary keys instead of key combinations.
For example:
Employee
Department
Name
ManagerOfDepartment
Development department
Mark
Jenny
3NF: conforms to 2NF; and there is no transitive dependency.
Analysis: column An in the same table depends on column B, and column B depends on column C.
Solution: move the columns involving transfer function dependencies out of the old table and save them in the new table.
For example:
Customer
Name
Phone
Address
ZipCode
Mark
1273283
Guangzhou × × ×
510000
Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.
Views: 0
*The comments in the above article only represent the author's personal views and do not represent the views and positions of this website. If you have more insights, please feel free to contribute and share.
Continue with the installation of the previous hadoop.First, install zookooper1. Decompress zookoope
"Every 5-10 years, there's a rare product, a really special, very unusual product that's the most un
© 2024 shulou.com SLNews company. All rights reserved.