Mysql database design

Database design concept

Database design is based on the specific needs of the business system , Combined with our choice of DBMS, Construct the optimal data storage model for this business system .

Establishment of database Table structure as well as The relationship between tables The process of .

Database design steps

Demand analysis （ What is the data ？ What attributes does the data have ？ What are the characteristics of data and attributes ？）

logic analysis （ adopt ER Figure to model the database logically , There is no need to consider the database management system we choose ）

physical design （ According to the characteristics of the database itself, the logical design is transformed into physical design ）

Maintenance design （1、 Create a table for new requirements ;2、 Table optimization ）

Table relations

1、 one-on-one ： Such as user and user details

One to one relationships are mostly used for table splitting , Put the frequently used fields in an entity into a table , Less frequently used fields are placed in another table , For lifting Query performance

Realization way ： Add foreign keys on either side , Associate another party's primary key , And set the foreign key to be unique （unique）

Take the user table for example ：

create table tb_user_desc (
id int primary key auto_increment,
city varchar(20),
edu varchar(10),
income int,
status char(2),
des varchar(100)
);
create table tb_user (
id int primary key auto_increment,
photo varchar(100),
nickname varchar(50),
age int,
gender char(1),
desc_id int unique,
--  Add foreign keys 
CONSTRAINT fk_user_desc FOREIGN KEY(desc_id) REFERENCES tb_user_desc(id)
);

2、 One to many ： Such as departments and employees

A Department corresponds to multiple employees , An employee can only correspond to one department .

Realization way ： Add a foreign key to more than one party , A primary key that points to a party of one

--  Departmental table 
CREATE TABLE tb_dept(
id int primary key auto_increment,
dep_name varchar(20),
addr varchar(20)
);
--  The employee table 
CREATE TABLE tb_emp(
id int primary key auto_increment,
name varchar(20),
age int,
dep_id int,
--  Add foreign keys  dep_id, relation  dept  Tabular id Primary key 
CONSTRAINT fk_emp_dept FOREIGN KEY(dep_id) REFERENCES tb_dept(id)
);

3、 Many to many ： Such as goods and orders

One item corresponds to multiple orders , An order contains multiple items

Realization way ： Create a third intermediate table , The middle table contains at least two foreign keys , Associate the primary keys of two parties respectively

Take order table and commodity table as an example

 

--  The order sheet 
CREATE TABLE tb_order(
id int primary key auto_increment,
payment double(10,2),
payment_type TINYINT,
status TINYINT
);
--  Commodity list 
CREATE TABLE tb_goods(
id int primary key auto_increment,
title varchar(100),
price double(10,2)
);
--  Intermediate table of order goods 
CREATE TABLE tb_order_goods(
id int primary key auto_increment,
order_id int,
goods_id int,
count int
);

--  After building the table , Add foreign keys 
alter table tb_order_goods add CONSTRAINT fk_order_id FOREIGN key(order_id) REFERENCES
tb_order(id);
alter table tb_order_goods add CONSTRAINT fk_goods_id FOREIGN key(goods_id) REFERENCES
tb_goods(id);