Multi table operation inner join query

• Catalog

  Multi table query classification

  Multi table query data preparation

  Query principle

  The query syntax

  Relevant concepts

  Example operation

  ---

• Multi table query classification

• Internal connection query
• External connection query
• Subquery
• Self association query

• Multi table query data preparation

• Create a total of 5 Tables
• They are user tables , The order sheet , Classification list , Commodity list , In the middle of table
• 
• 
• 
• 

• --  establish user surface 
  CREATE TABLE user(
  	id INT PRIMARY KEY auto_increment, --  user id
  	name VARCHAR(20),  --  User name 
  	age INT  --  User age 
  );
  --  Add data 
  INSERT INTO user VALUES (1,' Zhang San ',23);
  INSERT INTO user VALUES (2,' Li Si ',24);
  INSERT INTO user VALUES (3,' Wang Wu ',25);
  INSERT INTO user VALUES (4,' Zhao Liu ',26);
  
  --  Create order form 
  CREATE TABLE orderlist(
   id INT PRIMARY KEY auto_increment, --  Order id
   number VARCHAR(20),   --  The order no. 
   uid INT, --  Foreign key field 
   CONSTRAINT ou FOREIGN KEY (uid) REFERENCES user(id)
   );
   --  Add data 
   INSERT INTO orderlist VALUES (1,'hm001',1);
   INSERT INTO orderlist VALUES (2,'hm002',1);
   INSERT INTO orderlist VALUES (3,'hm003',2);
   INSERT INTO orderlist VALUES (4,'hm004',2);
   INSERT INTO orderlist VALUES (5,'hm005',3);
   INSERT INTO orderlist VALUES (6,'hm006',3);
   INSERT INTO orderlist VALUES (7,'hm007',NULL);
   
   --  Create commodity classification table 
   CREATE TABLE category(
     id INT PRIMARY KEY auto_increment, --  Classification of goods id
  	 NAME VARCHAR(20)  --  Category name 
   );
   --  Add data 
   INSERT INTO category VALUES (1,' Mobile phone digital ');
   INSERT INTO category VALUES (2,' Computer office ');
   INSERT INTO category VALUES (3,' Tobacco, wine, tea and sugar ');
   INSERT INTO category VALUES (4,' Shoes and bags ');
   
   --  Create a product list 
   CREATE TABLE product(
  		id INT PRIMARY KEY auto_increment, --  goods id
  		NAME VARCHAR(20), --  Name of commodity 
  		cid INT, --  Foreign key field 
  		CONSTRAINT cp_1 FOREIGN KEY (cid) REFERENCES category(id)
   );
   --  Add data 
   INSERT INTO product VALUES (1,' Huawei mobile phones ',1);
   INSERT INTO product VALUES (2,' Mi phones ',1);
   INSERT INTO product VALUES (3,' Lenovo computer ',2);
   INSERT INTO product VALUES (4,' Apple computer ',2);
   INSERT INTO product VALUES (5,' Chinese cigarettes ',3);
   INSERT INTO product VALUES (6,' Yuxi cigarette ',3);
   INSERT INTO product VALUES (7,' Family planning supplies ',NULL);
   
   --  Create middle table 
   CREATE TABLE us_pro(
  	upid INT PRIMARY KEY auto_increment, --  In the middle of table id
  	uid INT, --  Foreign key field , It needs to be associated with the primary key of the user table 
  	pid INT, --  Foreign key field , It needs to be associated with the primary key of the commodity table 
  	CONSTRAINT up_1 FOREIGN KEY (uid) REFERENCES user(id),
  	CONSTRAINT up_2 FOREIGN KEY (pid) REFERENCES product(id)
   );
   --  Add data 
   INSERT INTO us_pro VALUES (NULL,1,1);
   INSERT INTO us_pro VALUES (NULL,1,2);
   INSERT INTO us_pro VALUES (NULL,1,3);
   INSERT INTO us_pro VALUES (NULL,1,4);
   INSERT INTO us_pro VALUES (NULL,1,5);
   INSERT INTO us_pro VALUES (NULL,1,6);
   INSERT INTO us_pro VALUES (NULL,1,7);
   INSERT INTO us_pro VALUES (NULL,2,1);
   INSERT INTO us_pro VALUES (NULL,2,2);
   INSERT INTO us_pro VALUES (NULL,2,3);
   INSERT INTO us_pro VALUES (NULL,2,4);
   INSERT INTO us_pro VALUES (NULL,2,5);
   INSERT INTO us_pro VALUES (NULL,2,6);
   INSERT INTO us_pro VALUES (NULL,2,7);
   INSERT INTO us_pro VALUES (NULL,3,1);
   INSERT INTO us_pro VALUES (NULL,3,2);
   INSERT INTO us_pro VALUES (NULL,3,3);
   INSERT INTO us_pro VALUES (NULL,3,4);
   INSERT INTO us_pro VALUES (NULL,3,5);
   INSERT INTO us_pro VALUES (NULL,3,6);
   INSERT INTO us_pro VALUES (NULL,3,7);
   INSERT INTO us_pro VALUES (NULL,4,1);
   INSERT INTO us_pro VALUES (NULL,4,2);
   INSERT INTO us_pro VALUES (NULL,4,3);
   INSERT INTO us_pro VALUES (NULL,4,4);
   INSERT INTO us_pro VALUES (NULL,4,5);
   INSERT INTO us_pro VALUES (NULL,4,6);
   INSERT INTO us_pro VALUES (NULL,4,7);

• Query principle

• Inner join queries are part of the data where two tables intersect ( Data associated with primary and foreign keys )

• The query syntax

• Explicit inner connection
• select Name from Table name 1 [inner] join Table name 2 on Conditions
• Implicit inner join
• select Name from Table name 1, Table name 2 where Conditions

• Relevant concepts

• Self join
• Concept ： It is a special equivalent connection in inner connection query , The so-called self connection refers to the connection between a table and its current table
• The biggest feature ： One table is regarded as two tables
• Connect yourself
• Equivalent connection
• Is in the keyword on The matching condition after is through = To achieve ;
• Equivalent connection is usually a table connecting another table
• Unequal value connection
• In keywords on Use in the post matching condition except = Inequality conditions implemented by relational operators other than (> >= < <= !=)

• Example operation

• Explicit inner connection
• Query user information and corresponding order information
• Query user information and corresponding order information , names
• Query user name , Age and order number
• 

• --  Explicit inner connection 
  --  Query user information and corresponding order information 
  SELECT * FROM user INNER JOIN orderlist ON orderlist.uid=user.id;
  
  --  Query user information and corresponding order information , names 
  SELECT * FROM user u INNER JOIN orderlist o ON o.uid=u.id;
  
  --  Query user name , Age and order number 
  SELECT
  		u.name,      --  User name 
  		u.age,       --  User age 
  		o.number     --  The order no. 
  FROM
      user u       --  User table 
  INNER JOIN
      orderlist o  --  The order sheet 
  ON 
  		o.uid=u.id;

• Implicit inner join
• Query user name , Age and order number
• 

• --  Implicit inner join 
  --  Query user name , Age and order number 
  SELECT
  		u.name,      --  User name 
  		u.age,       --  User age 
  		o.number     --  The order no. 
  FROM
      user u,       --  User table 
      orderlist o  --  The order sheet 
  WHERE
  		o.uid=u.id;