INNER JOIN in SQL

Joins in SQL are used to combine rows from two or more tables based on a related column between them.

The most common types of joins are:

INNER JOIN,
LEFT JOIN,
RIGHT JOIN, and
FULL OUTER JOIN

The INNER JOIN keyword selects records that have matching values in both tables.

SQL Syntax

SELECT columns
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;

Or alternatively,

SQL Syntax

SELECT columns
FROM table1
JOIN table2
ON table1.column_name = table2.column_name;

Note: Using JOIN without specifying the type of join defaults to an INNER JOIN.

Example: Let's use two tables: employees and departments.

SQL

-- Creating the employee table
CREATE TABLE employees (
    employee_id INT PRIMARY KEY,
    first_name VARCHAR(50),
    department_id INT
);

-- Inserting the provided data
INSERT INTO employees
VALUES 
(1, 'Ashish', 1),
(2, 'Rahul', 2),
(3, 'Priya', 1),
(4, 'Sneha', 3),
(5, 'Shweta', 4);

Table: employees

Employee ID	First Name	Department ID
1	Ashish	1
2	Rahul	2
3	Priya	1
4	Sneha	3
5	Shweta	4

SQL

-- Creating the departments table
CREATE TABLE departments (
    department_id INT PRIMARY KEY,
    department_name VARCHAR(50)
);

-- Inserting the provided data
INSERT INTO departments
VALUES 
(1, 'Sales'),
(2, 'Marketing'),
(3, 'HR');

Table: departments

Department_ID	Department_Name
1	Sales
2	Marketing
3	HR

SQL

SELECT e.employee_id, e.first_name, e.department_id, d.department_name
FROM employees e
Inner JOIN departments d ON e.department_id = d.department_id;

The above query returns the following result:

Employee_ID	First_Name	Department_ID	Department_Name
1	Ashish	1	Sales
2	Rahul	2	Marketing
3	Priya	1	Sales
4	Sneha	3	HR

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