Inner Join (Clause)

Definition

INNER JOIN is a SQL clause used to combine rows from two or more tables based on a matching condition (join predicate). It returns only the intersection of matching records.

What Problem It Solves

Solves the issue of data retrieval across normalized tables by linking related data using primary key–foreign key relationships.

What Happens If Not Used

You may get incomplete or unrelated data, or you would need multiple separate queries and manual merging, increasing complexity and inefficiency.

Easy Wording

Shows only the rows where both tables have matching values.

Technical Example

A customer list and an order list: INNER JOIN shows only customers who have actually placed orders. SELECT Customers.name, Orders.order_id
FROM Customers
INNER JOIN Orders
ON Customers.customer_id = Orders.customer_id;