Khóa học miễn phí MySQL – Right Join nhận dự án làm có lương

MySQL – Right Join

Table of content


MySQL Right Join

The Right Join or Right Outer Join query in MySQL returns all rows from the right table, even if there are no matches in the left table. So, if zero records are matched in the left table, the right join will still return a row in the result, but with a NULL value in each column of the left table.

In short, a right join returns all the values from the right table, plus matched values from the left table or NULL in case of no matching join predicate.

Right Join

The resultant table displayed after implementing the Right Join is not stored anywhere in the database.

Syntax

Following is the basic syntax of Right Join in SQL −

SELECT table1.column1, table2.column2...
FROM table1
RIGHT JOIN table2
ON table1.common_field = table2.common_field;

Example

Assume we are creating a table named CUSTOMERS, which contains the personal details of customers including their name, age, address and salary etc.

CREATE TABLE CUSTOMERS (
   ID INT NOT NULL,
   NAME VARCHAR (20) NOT NULL,
   AGE INT NOT NULL,
   ADDRESS CHAR (25),
   SALARY DECIMAL (18, 2),       
   PRIMARY KEY (ID)
);

Now insert values into this table using the INSERT statement as follows −

INSERT INTO CUSTOMERS VALUES
(1, ''Ramesh'', 32, ''Ahmedabad'', 2000.00 ),
(2, ''Khilan'', 25, ''Delhi'', 1500.00 ),
(3, ''Kaushik'', 23, ''Kota'', 2000.00 ),
(4, ''Chaitali'', 25, ''Mumbai'', 6500.00 ),
(5, ''Hardik'', 27, ''Bhopal'', 8500.00 ),
(6, ''Komal'', 22, ''Hyderabad'', 4500.00 ),
(7, ''Muffy'', 24, ''Indore'', 10000.00 );

The table will be created as −

ID NAME AGE ADDRESS SALARY
1 Ramesh 32 Ahmedabad 2000.00
2 Khilan 25 Delhi 1500.00
3 Kaushik 23 Kota 2000.00
4 Chaitali 25 Mumbai 6500.00
5 Hardik 27 Bhopal 8500.00
6 Komal 22 Hyderabad 4500.00
7 Muffy 24 Indore 10000.00

Let us create another table ORDERS, containing the details of orders made and the date they are made on.

CREATE TABLE ORDERS (
   OID INT NOT NULL,
   DATE VARCHAR (20) NOT NULL,
   CUSTOMER_ID INT NOT NULL,
   AMOUNT DECIMAL (18, 2),
);

Using the INSERT statement, insert values into this table as follows −

INSERT INTO ORDERS VALUES 
(102, ''2009-10-08 00:00:00'', 3, 3000.00),
(100, ''2009-10-08 00:00:00'', 3, 1500.00),
(101, ''2009-11-20 00:00:00'', 2, 1560.00),
(103, ''2008-05-20 00:00:00'', 4, 2060.00);

The table is displayed as follows −

OID DATE CUSTOMER_ID AMOUNT
102 2009-10-08 00:00:00 3 3000.00
100 2009-10-08 00:00:00 3 1500.00
101 2009-11-20 00:00:00 2 1560.00
103 2008-05-20 00:00:00 4 2060.00

Right join Query

Now, let us join these two tables using the Right Join query as follows.

SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;

Output

This would produce the following result −

ID NAME AMOUNT DATE
3 Kaushik 3000.00 2009-10-08 00:00:00
3 Kaushik 1500.00 2009-10-08 00:00:00
2 Khilan 1560.00 2009-11-20 00:00:00
4 Chaitali 2060.00 2008-05-20 00:00:00

Joining Multiple Tables with Right Join

Like Left Join, Right Join also joins multiple tables. However, the contrast occurs where the second table is returned as a whole instead of the first.

Syntax

Following is the syntax to join multiple tables using Right Join −

SELECT column1, column2, column3...
FROM table1
RIGHT JOIN table2
ON table1.column_name = table2.column_name
RIGHT JOIN table3
ON table2.column_name = table3.column_name
.
.
.

Example

Here, let us consider the previously created tables CUSTOMERS and ORDERS; along with the newly created table EMPLOYEE.

We will create the EMPLOYEE table using the query below −

CREATE TABLE EMPLOYEE (
   EID INT NOT NULL,
   EMPLOYEE_NAME VARCHAR (30) NOT NULL,
   SALES_MADE DECIMAL (20)
);

Now, we can insert values into this empty tables using the INSERT statement as follows −

INSERT INTO EMPLOYEE VALUES
(102, ''SARIKA'', 4500),
(100, ''ALEKHYA'', 3623),
(101, ''REVATHI'', 1291),
(103, ''VIVEK'', 3426);

The table is created as −

EID EMPLOYEE_NAME SALES_MADE
102 SARIKA 4500
100 ALEKHYA 3623
101 REVATHI 1291
103 VIVEK 3426

Let us join these three tables using the Right Join query given below −

SELECT CUSTOMERS.ID, CUSTOMERS.NAME, ORDERS.DATE, EMPLOYEE.EMPLOYEE_NAME
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
RIGHT JOIN EMPLOYEE
ON ORDERS.OID = EMPLOYEE.EID;

Through this query, we are trying to display the records of Customer IDs, Customer names, Orders made on specific dates and names of the employees that sold them.

Output

The resultant table is obtained as follows −

ID NAME DATE EMPLOYEE_NAME
3 Kaushik 2009-10-08 00:00:00 SARIKA
3 Kaushik 2009-10-08 00:00:00 ALEKHYA
2 Khilan 2009-11-20 00:00:00 REVATHI
4 Chaitali 2008-05-20 00:00:00 VIVEK

Right Join with WHERE Clause

A WHERE Clause is used to filter out records that satisfy the condition specified by it. This clause can be used with the Right Join technique to apply constraints on the result-set obtained.

Syntax

The syntax of Right Join when used with WHERE clause is given below −

SELECT column_name(s)
FROM table_name1
RIGHT JOIN table_name2
ON table_name1.column_name = table_name2.column_name
WHERE condition

Example

Records in the combined database tables can be filtered using the WHERE clause. Consider the previous two tables CUSTOMERS and ORDERS; and join them using the following query −

SELECT ID, NAME, DATE, AMOUNT FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
WHERE ORDERS.AMOUNT > 1000.00;

Output

The resultant table is obtained as follows −

ID NAME DATE Amount
3 Kaushik 2009-10-08 00:00:00 3000.00
3 Kaushik 2009-10-08 00:00:00 1500.00
2 Khilan 2009-11-20 00:00:00 1560.00
4 Chaitali 2008-05-20 00:00:00 2060.00

Right Join Using a Client Program

We can also perform the Right join operation on one or more tables using a client program.

Syntax

To join two tables using right join through a PHP program, we need to execute the SQL query with RIGHT JOIN clause using the mysqli function query() as follows −

$sql = ''SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a RIGHT JOIN tcount_tbl b 
ON a.tutorial_author = b.tutorial_author
$mysqli->query($sql);

To join two tables using right join through a JavaScript program, we need to execute the SQL query with RIGHT JOIN clause using the query() function of mysql2 library as follows −

sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a RIGHT JOIN tcount_tbl b 
ON a.tutorial_author = b.tutorial_author";
con.query(sql);  

To join two tables using right join through a Java program, we need to execute the SQL query with RIGHT JOIN clause using the JDBC function executeQuery() as follows −

String sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a RIGHT JOIN tcount_tbl b 
ON a.tutorial_author = b.tutorial_author";
st.executeQuery(sql);

To join two tables using right join through a python program, we need to execute the SQL query with RIGHT JOIN clause using the execute() function of the MySQL Connector/Python as follows −

right_join_query = "SELECT ID, NAME, AMOUNT, DATE FROM CUSTOMERS RIGHT JOIN ORDERS ON CUSTOMERS.ID = ORDERS.CUST_ID"
cursorObj.execute(right_join_query)

Example

Following are the programs −

$dbhost = ''localhost
$dbuser = ''root
$dbpass = ''password
$dbname = ''TUTORIALS
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if ($mysqli->connect_errno) {
    printf("Connect failed: %s
", $mysqli->connect_error); exit(); } // printf(''Connected successfully.
''); $sql = ''SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a RIGHT JOIN tcount_tbl b ON a.tutorial_author = b.tutorial_author $result = $mysqli->query($sql); if ($result->num_rows > 0) { echo " following is the both table details after executing right join! n"; while ($row = $result->fetch_assoc()) { printf( "Id: %s, Author: %s, Count: %d", $row["tutorial_id"], $row["tutorial_author"], $row["tutorial_count"] ); printf("n"); } } else { printf(''No record found.
''); } mysqli_free_result($result); $mysqli->close();

Output

The output obtained is as follows −

following is the both table details after executing right join!
Id: , Author: , Count: 20
Id: , Author: , Count: 5
Id: , Author: , Count: 4
Id: , Author: , Count: 20
Id: , Author: , Count: 1
Id: 3, Author: Sanjay, Count: 1    
var mysql = require("mysql2");
var con = mysql.createConnection({
  host: "localhost",
  user: "root",
  password: "password",
}); //Connecting to MySQL

con.connect(function (err) {
  if (err) throw err;
  //   console.log("Connected successfully...!");
  //   console.log("--------------------------");
  sql = "USE TUTORIALS";
  con.query(sql);

  //Right Join
  sql =
    "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a RIGHT JOIN tcount_tbl b ON a.tutorial_author = b.tutorial_author";
  con.query(sql, function (err, result) {
    if (err) throw err;
    console.log(result);
  });
});     

Output

The output produced is as follows −

[
   { tutorial_id: null, tutorial_author: null, tutorial_count: 20 },
   { tutorial_id: null, tutorial_author: null, tutorial_count: 5 },
   { tutorial_id: null, tutorial_author: null, tutorial_count: 4 },
   { tutorial_id: null, tutorial_author: null, tutorial_count: 20 },
   { tutorial_id: null, tutorial_author: null, tutorial_count: 1 },
   { tutorial_id: null, tutorial_author: null, tutorial_count: 1 },
   { tutorial_id: 1, tutorial_author: ''John Poul'', tutorial_count: 2 }
]
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class RightJoin {
   public static void main(String[] args) {
      String url = "jdbc:mysql://localhost:3306/TUTORIALS";
      String username = "root";
      String password = "password";
      try {
         Class.forName("com.mysql.cj.jdbc.Driver");
         Connection connection = DriverManager.getConnection(url, username, password);
         Statement statement = connection.createStatement();
         System.out.println("Connected successfully...!");

         //MySQL RIGHT JOIN...!;
         String sql = "SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count FROM tutorials_tbl a RIGHT JOIN tcount_tbl b ON a.tutorial_author = b.tutorial_author";
         ResultSet resultSet = statement.executeQuery(sql);
         System.out.println("Table records after LEFT Join...!");
         while (resultSet.next()){
            System.out.println(resultSet.getString(1)+ " "+ resultSet.getString(2)+" "+resultSet.getString(3));
         }
         connection.close();
      } catch (Exception e) {
         System.out.println(e);
      }
   }
}   

Output

The output obtained is as shown below −

Connected successfully...!
Table records after LEFT Join...!
null null 20
null null 5
null null 4
null null 20
1 John Paul 1
3 Sanjay 1
import mysql.connector
#establishing the connection
connection = mysql.connector.connect(
    host=''localhost'',
    user=''root'',
    password=''password'',
    database=''tut''
)
cursorObj = connection.cursor()
right_join_query = f"""
SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUST_ID
"""
cursorObj.execute(right_join_query)
# Fetching all the rows that meet the criteria
filtered_rows = cursorObj.fetchall()
for row in filtered_rows:
    print(row)
cursorObj.close()
connection.close()         

Output

Following is the output of the above code −

(3, ''kaushik'', 3000, ''2009-10-08 00:00:00'')
(3, ''kaushik'', 1500, ''2009-10-08 00:00:00'')
(2, ''Khilan'', 1560, ''2009-11-20 00:00:00'')
(4, ''Chaital'', 2060, ''2008-05-20 00:00:00'')

Khóa học lập trình tại Toidayhoc vừa học vừa làm dự án vừa nhận lương: Khóa học lập trình nhận lương tại trung tâm Toidayhoc