SQL INNER JOIN Keyword

The INNER JOIN keyword is used in SQL to combine rows from two or more tables based on a related column between them. It only returns rows where there's a match in both tables.

INNER JOIN: Definition and Usage

Imagine you have two tables: one with customer details and another with their orders. INNER JOIN lets you efficiently combine these tables to show customer information alongside their corresponding orders. If an order doesn't have a matching customer, or vice-versa, that row is excluded from the result.

Syntax

The basic syntax looks like this:

SELECT column_names
FROM table1
INNER JOIN table2 ON table1.column_name = table2.column_name;
      

Examples

Joining Two Tables

This example combines the 'Orders' and 'Customers' tables to retrieve order IDs and customer names.

SELECT Orders.OrderID, Customers.CustomerName
FROM Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;
      

OrderID | CustomerName
-----------------------
1       | John Doe
2       | Jane Smith
      

Joining Multiple Tables

INNER JOIN can be used multiple times to combine data from more than two tables. This example adds shipper information to the previous query.

SELECT Orders.OrderID, Customers.CustomerName, Shippers.ShipperName
FROM Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID
INNER JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID;
      

OrderID | CustomerName | ShipperName
------------------------------------
1       | John Doe      | Speedy Express
2       | Jane Smith    | Fast Delivery