Mysql database Chapter 1 Summary

Basic concepts of database

What is database design ？

Database design is to integrate the data entities in the database and the relationship between these data entities , The process of planning and structuring

What are some aspects of good database design

1. Efficient
2. For further expansion
3. It can be that application development becomes easier

The steps to design a database ：

1. Demand analysis stage ： Analyze customers' business and data processing requirements
2. Outline design stage ： Drawing database E-R The diagram is used to communicate between the internal designers of the project team and the customers , Confirm the correctness and completeness of the requirement information
3. Detailed design stage ： take E-R Convert graph to multiple tables , Carry out logical design , Confirm the main foreign key of each table and apply the three paradigms of database design
4. Code writing
5. Run the test
6. Deploy online

Regardless of the size and complexity of the database, we can refer to the following basic steps ：

1. To collect information
2. Identifying entities
3. Identify the details that each entity needs to store , Identity is an attribute of an entity
4. Identify the relationship between entities

What is an entity ：

Entities are generally nouns , An entity only describes one thing , Entities with the same meaning cannot be repeated .
Each different entity in the database has a corresponding table .

What is an attribute

Simply speaking , That is, the sub member information attribute contained in each entity subdivided is the column name in the entity , Each entity corresponds to a table , Each child member in the entity corresponds to each column in the table
Be careful ： When decomposing entity attributes , Member information with the same meaning cannot be repeated

Identify the relationship between entities ：

The relationship between entities

Database type

Relational database

The storage format can directly reflect the relationship between entities , Similar to the table created , There are complex relationships between tables .
Oracle 、Mysql 、DB2 、Microsoft SQL Server、 Microsoft Access etc.

Non relational database

Refers to distributed 、 Non relational 、 There is no guarantee that ACID Principle of data storage system .
MongoDb 、 redis 、 HBase、 Cloudant etc.

E-R chart

E-R（Entity-Relationship） Entity relation diagram

Entity

The so-called entity refers to the things in the world that have the characteristics and attributes to distinguish other things and are connected with other things .
An entity is a row of specific data in a table .
We often refer to the entire table as an entity .

attribute

Attribute corresponds to the column in the table , Can be understood as the characteristics of entities

contact

A relationship is an association between two or more entities
Entity set , rectangular
attribute , The ellipse
Contact set , The diamond
Connect attributes and entity sets or entity sets and association sets , A straight line

Mapping cardinality

The mapping cardinality represents the number of other entities associated with the entity by association , Corresponding entity set x and y The binary relationship between
one-on-one （1:1）：x One of the entities in is at most related to y An entity Association in .
One to many （1：n）：x One of the entities in can be associated with y Any number of entity associations in .
For one more （n：1）：x An entity in can be associated with at most y An entity Association in ,y One of the entities in can be associated with x Any number of entity associations in .
Many to many （m:n）：x One of the entities in can be associated with y Any number of entity associations in , vice versa .

Three paradigms

First normal form （Normal Formate ,1NF)

The goal of the first paradigm is to ensure the atomicity of each column . If each column （ Or each attribute value ） Are indivisible minimum data units （ Also known as the smallest atomic unit ）, The first paradigm .

Second normal form （2NF）

On the basis of the first paradigm, go one step further , The goal is to ensure that every column in the table is related to the primary key , If the first relation satisfies the first normal form , And all columns except the primary key depend on the primary key , The second paradigm is satisfied
Just describe one thing

Third normal form （3NF）

Follow up on the second paradigm , The goal of the third paradigm is to ensure that each column is directly related to the primary key column , Not indirectly , If the first relation satisfies the second normal form , Besides the primary key, other columns can only depend on the primary key column , There is no interdependency between columns , The third paradigm is satisfied
Simply speaking , It depends on the primary key , Changes with the primary key , When the primary key changes, the contents of the column also change .