Inner Join

An INNER JOIN returns only the rows where there is a match in both tables being joined - it's the most commonly used join type, and the default when you write JOIN without specifying a type.

Basic Syntax

SELECT c.first_name, o.amount
FROM customers c
INNER JOIN orders o ON c.customer_id = o.customer_id;

This returns only customers who have placed at least one order - customers with no orders, and orders with no matching customer, are excluded from the result.

Joining Multiple Tables

SELECT c.first_name, o.order_id, p.product_name
FROM customers c
INNER JOIN orders o ON c.customer_id = o.customer_id
INNER JOIN order_items oi ON o.order_id = oi.order_id
INNER JOIN products p ON oi.product_id = p.product_id;

When to Use an Inner Join

Use an inner join when you only care about records that have a confirmed relationship on both sides - for example, only showing customers who have actually placed orders.