SQL Inner Join

INNER JOIN in SQL is the most common and important type of join which allows users to access matching data from two or more database tables.

When the join condition is met between the tables, then it returns all the common rows from them.

The Venn diagram of INNER JOIN is shown in the following picture. The shaded region of the Venn diagram shows the intersection values of two tables:

Syntax of INNER JOIN in SQL

SELECT Column_Name1, Column_Name2, ….., Column_NameN
FROM Table_Name1 INNER JOIN Table_Name2
ON Table_Name1.Column_Name = Table_Name2.Column_Name;

Example of Inner Join in SQL

Let's take two tables named Employee_Details and Department to understand the concept of INNER JOIN. The Employee_Details table contains Emp_ID, Emp_Name, Dept_ID, and Emp_Salary columns. The Department table contains Dept_Id and Dept_Name columns.

We can check the data of Employee_Details and Department table using the following two different queries:

Output:

Dept_Id	Dept_Name
1001	Finance
1002	Marketing
1003	Sales
1004	Coding
1005	Administration

Output:

Emp_Id	Emp_Name	Dept_Id	Emp_Salary
1	Akshay	1001	23000
2	Ram	1002	24000
3	Balram	1004	25000
4	Yatin	NULL	NULL
5	Manoj	1004	23000
6	Sheetal	1003	24000
8	Yogesh	NULL	NULL
9	Naveen	NULL	NULL
10	Tarun	1004	23000

The following query joins these above two tables using INNER JOIN in structured Query Language:

SELECT 
Employee_Details.Emp_Id, 
Employee_Details.Emp_Name, Department.Dept_Name, Employee_Details.Emp_Salary, 

FROM Department INNER JOIN Employee_Details 

ON 
Department.Dept_ID = Employee_Details.Emp_Id; 

Explanation of above INNER JOIN query:

This query joins the Employee_Details and Department table and accesses the records from both the tables where Department.Dept_Id = Employee_Details.DeptId.

It only fetches the details of those employees from both the tables whose Dept_Id in the Employee table matches with the Dept_Id of the Department table.

If the Dept_Id is NULL or not matching, then that row would not show in the output.

Output: