SQL INNER JOIN Explained with Examples + Practice Questions

When to Use INNER JOIN

Use INNER JOIN when you want only matching data from two tables.

It returns rows where the join condition is satisfied in both tables.

This is one of the most important SQL topics for interviews.

Example Dataset

Table: employees

Table: departments

What is INNER JOIN

INNER JOIN combines rows from two tables based on a related column.

Basic Syntax

sql
SELECT columns
FROM table1
INNER JOIN table2
ON table1.column = table2.column;

Example: Join Employees with Departments

sql
SELECT employees.name, departments.department_name
FROM employees
INNER JOIN departments
ON employees.department_id = departments.id;

Output:

• John -> HR
• Alice -> IT
• Bob -> IT
• Emma -> Finance

David is excluded because department_id is NULL.

Using Table Aliases

sql
SELECT e.name, d.department_name
FROM employees e
INNER JOIN departments d
ON e.department_id = d.id;

Selecting Multiple Columns

sql
SELECT e.name, d.department_name, e.salary
FROM employees e
INNER JOIN departments d
ON e.department_id = d.id;

INNER JOIN with WHERE

sql
SELECT e.name, d.department_name
FROM employees e
INNER JOIN departments d
ON e.department_id = d.id
WHERE d.department_name = 'IT';

Key Concepts

• INNER JOIN returns only matching rows
• Rows without matches are excluded
• Requires a join condition using ON
• Aliases improve readability
• Most interview problems use JOIN + filtering

INNER JOIN Flow (Concept)

• Match rows where keys are equal
• Combine columns from both tables
• Ignore unmatched rows

Common Questions (FAQ)

What does INNER JOIN do

INNER JOIN returns only rows where there is a match in both tables.

What happens to unmatched rows

They are excluded from the result.

Why use aliases in JOIN

Aliases make queries shorter and easier to read.

Is INNER JOIN same as JOIN

Yes, JOIN by default means INNER JOIN.

Internal Learning Links

• Learn SELECT basics
• Learn WHERE filtering
• Learn GROUP BY
• Learn OUTER JOIN

Practice CTA

Practice SQL JOIN questions on Schoolabe to master real interview scenarios.