SQL Inner Join

INNER JOIN returns rows that have matching values in both tables. It is the most commonly used join type.

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SQL INNER JOIN

INNER JOIN returns only the rows where there is a match in both joined tables. It is the most commonly used type of JOIN.

Basic Syntax

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

Example: Customers and Orders

SELECT c.name, o.order_date
FROM customers AS c
INNER JOIN orders AS o
  ON c.id = o.customer_id;

This query returns only customers who have placed at least one order.

How INNER JOIN Works

Think of INNER JOIN as the intersection of two tables. Only matching rows are included in the result.

Primary Key and Foreign Key

INNER JOIN commonly connects a primary key in one table with a foreign key in another.

customers.id (Primary Key)
orders.customer_id (Foreign Key)

INNER JOIN with WHERE

You can filter results after joining tables.

SELECT c.name, o.order_date
FROM customers AS c
INNER JOIN orders AS o
  ON c.id = o.customer_id
WHERE o.order_date > '2026-01-01';

Joining More Than Two Tables

You can chain multiple INNER JOINs.

SELECT c.name, o.order_date, p.name AS product_name
FROM customers AS c
INNER JOIN orders AS o
  ON c.id = o.customer_id
INNER JOIN products AS p
  ON o.product_id = p.id;

NULL Behavior

Rows with NULL values in the join column will not match and will not appear in the result.

Common Mistakes

Forgetting the ON condition
Joining on the wrong column
Creating unintended duplicates due to one-to-many relationships

Performance Note

Indexes on join columns (especially foreign keys) significantly improve performance for INNER JOIN queries.

Next Step

Continue with SQL LEFT JOIN to learn how to return all rows from the left table even if there is no match.

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SQL Left Join →