MySQL Database Design notes and summaries (2) logical design

"Example Demo-the relationship between entities"

"The work of logical design"

① the logical model of transforming demand into a database

② the logical model in the form of ER diagrams

③ is independent of the specific DBMS system chosen

"Noun explanation"

The candidate code can be simply understood as the primary key or unique index of the database

Main code is primary key

"ER legend description"

"ER diagram example-small e-commerce website"

"Overview of Design Paradigms"

Common database design paradigms include: first paradigm , second Paradigm , third paradigm and BC paradigm , fourth normal form and fifth paradigm.

"Database operation exception and data redundancy"

Data redundancy: The same data exists in multiple places, or a column in a table can be computed by other columns.

"First paradigm (1NF)"

"Second normal form (2NF)"

Therefore, the above table design does not conform to the second normal form requirement

Problems that exist:

A Insert exception

B Delete exception

C Update exception

D Data Redundancy

"Third paradigm (3NF)"

Classification and classification descriptions do not conform to the requirements of the third paradigm.

"BC paradigm (boyce.codd paradigm BCNF)"

How to resolve:

MySQL Database Design notes and summaries (2) logical design