MySQL foundation 04 MySQL architecture

Basic concepts :
• database : A database is a collection of related tables .
• Data sheet : A table is a matrix of data . A table in a database looks like a simple spreadsheet .
• Column : A column of ( data elements ) Contains the same type of data , For example, postal code data .
• That's ok ： a line （= Tuples , Or record ） It's a set of related data , For example, a data subscribed by a user .
• Primary key ： The primary key is unique . A data table can only contain one primary key . You can use the primary key to query data .
• Foreign keys ： Foreign keys are used to associate two tables .
MySQL Is a relational database (Relational Database Management System), This so-called " Relational type " You can understand
by " form " The concept of , A relational database consists of one or more tables , A table as shown in the figure :

Student information of a class

Logistics structure :

ER chart
Entity Is the data object in the data model , For example, in e-commerce business , goods 、 Order 、 Categories can be used as a data object , draw The diagram is represented by a rectangle .

1 Yes 1(1:1),1 Yes 1 Relationships are for entities A And entities B Come on ,A There's only one B,B It can only correspond to one A.
1 For more than (1:N),1 Many refers to entities A It can correspond to multiple entities B, But entities B There's only one A.
Many to many (N:N), Many to many refers to entities A It can correspond to multiple entities B, Entity B It can also correspond to multiple entities A.