SQL INNER JOIN

An SQL Inner Join is the default type of JOIN.
In an SQL Inner Join, if there is data in Table A, and there is data in Table B the row will be joined.
If there are rows in Table A, but no matching row in Table B it will not be shown.
Also if there are no rows in Table A, but there are matching rows in Table B, it will not be shown.
For instance imagine that there are two tables. Employee and Department. Imagine that we have two tables, Employee and Department as given below.

Employee Table

Rambo

Robert

Mugambo

Satraj

Nagashekar

Rao

Tom

Harry

Dana

Laura

Rambo

Fox

Giselle

Chivvi

Chatur

Bansal

Consider the following Department table:

Department Table

Engineering

Management

Finance

Kitchen

Administration

Scenario: Get Employee First Name, Last Name and Department Name.
For the above scenario, we can join the two tables using the JOIN clause.

SELECT EMPLOYEE.FIRSTNAME, EMPLOYEE.LASTNAME, DEPARTMENT.DEPARTMENTNAME
	FROM EMPLOYEE INNER JOIN DEPARTMENT 
	ON EMPLOYEE.DEPARTMENTID = DEPARTMENT.DEPARTMENTID

Result:

Rambo

Robert

Engineering

Mugambo

Satraj

Engineering

Nagashekar

Rao

Management

Tom

Harry

Management

Dana

Laura

Kitchen

Rambo

Fox

Kitchen

Giselle

Chivvi

Finance

In the above SELECT Query, we inner joined two tables, Employee and Department based on foreign key, DEPARTMENTID.
By doing that, we are successfully able to show the department name also in the result.