Multi table operation - one to one, one to many and many to many

Catalog

one-on-one

Multi table introduction

one-on-one

Example operation

One to many

Introduce

Example operation

Many to many

Introduce

Demonstration of practical operation

---

• one-on-one

• Multi table introduction

• Multi table concept
• To put it bluntly, multiple data tables , There can be some association between tables , This association is achieved through foreign key constraints
• Classification of multiple tables
• one-on-one
• One to many
• Many to many

• one-on-one

• Applicable scenario
• People and ID cards ;
• A person has only one ID card , An ID card can only correspond to one person
• Principle of building table
• Create a foreign key in any table , To associate the primary key of another table

• Example operation

• 
• 

• --  establish person surface 
  CREATE TABLE person(
   id INT PRIMARY KEY auto_increment, --  Primary key id
    name VARCHAR(20) --  full name 
  );
  --  Add data 
  INSERT INTO person VALUES (NULL,' Zhang San '),(NULL,' Li Si ');
  --  establish card surface 
  CREATE TABLE card(
   id INT PRIMARY KEY auto_increment, --  Primary key id
   number VARCHAR(20) UNIQUE NOT NULL, --  ID number 
   pid INT UNIQUE, --  Foreign key column 
   CONSTRAINT ou FOREIGN KEY (pid) REFERENCES person(id)
  );
  --  Add data 
  INSERT INTO card VALUES (NULL,'12345',1),(NULL,'56789',2);

• One to many

• Introduce

• Applicable scenario
• Such as ：
• Users and orders ;
• A user can have multiple orders
• Commodity classification and commodity ;
• There can be multiple products under one category
• Principle of building table
• On the more side , Create foreign key constraints
• To associate a party's primary key

• Example operation

• The user is satisfied with the order
• 
• 

• --  establish user surface 
  CREATE TABLE user(
   id INT PRIMARY KEY auto_increment, --  Primary key id
    name VARCHAR(20) --  full name 
  );
  --  Add data 
  INSERT INTO user VALUES (NULL,' Zhang San '),(NULL,' Li Si ');
  --  establish orderlist surface 
  CREATE TABLE orderlist(
   id INT PRIMARY KEY auto_increment, --  Primary key id
   number VARCHAR(20), --  The order no. 
   uid INT, --  Foreign key column 
   CONSTRAINT ou FOREIGN KEY (uid) REFERENCES user(id)
  );
  --  Add data 
  INSERT INTO orderlist VALUES (NULL,'hm001',1),(NULL,'hm002',1),(NULL,'hm003',2),(NULL,'hm004',2);

• Commodity classification vs. commodity
• 
• 

• --  establish category surface 
  CREATE TABLE category(
   id INT PRIMARY KEY auto_increment, --  Primary key id
    name VARCHAR(20) --  Category name 
  );
  --  Add data 
  INSERT INTO category VALUES (NULL,' Mobile phone digital '),(NULL,' Computer office ');
  --  establish product surface 
  CREATE TABLE product(
   id INT PRIMARY KEY auto_increment, --  Primary key id
   number VARCHAR(30), --  Name of commodity 
   uid INT, --  Foreign key column 
   CONSTRAINT ou FOREIGN KEY (uid) REFERENCES category(id)
  );
  --  Add data 
  INSERT INTO product VALUES (NULL,'Sony xperia 1',1),(NULL,'Google pixel 6 pro',1),(NULL,'ROG  Mob ',2),(NULL,'MacBook pro',2);

• Many to many

• Introduce

• Applicable scenario
• Such as ：
• Students and courses
• A student can choose multiple courses
• A course can also be chosen by multiple students
• Principle of building table
• You need to use the third middle table , The middle table contains at least two columns
• These two columns act as foreign keys in the middle table , Associate the primary keys of the other two tables respectively

• Demonstration of practical operation

• 

• --  establish student class 
  CREATE TABLE student(
   id INT PRIMARY KEY auto_increment, --  Primary key id
   name VARCHAR(20) --  The student's name 
  );
  --  Add data 
  INSERT INTO student VALUES (NULL,' Zhang San '),(NULL,' Li Si ');
  
  --  establish course surface 
  CREATE TABLE course(
   id INT PRIMARY KEY auto_increment, --  Primary key id
   name VARCHAR(20) --  Course name 
  );
  --  Add data 
  INSERT INTO course VALUES (NULL,' Chinese language and literature '),(NULL,' mathematics ');
  
  --  Create middle table 
  CREATE TABLE stu_course(
   id INT PRIMARY KEY auto_increment, --  Primary key id
   sid INT, --  Used for and student In the table id Make foreign key constraints 
   cid INT, --  Used for and course In the table id Make foreign key constraints 
   CONSTRAINT sc_1 FOREIGN KEY (sid) REFERENCES	student(id), --  Add a foreign key constraint 
   CONSTRAINT sc_2 FOREIGN KEY (cid) REFERENCES	course(id) --  Add a foreign key constraint 
  );
  --  Add data 
  INSERT INTO stu_course VALUES (NULL,1,1),(NULL,1,2),(NULL,2,1),(NULL,2,2);