SQL INNER JOIN keyword (internal connection)
May 16, 2021 SQL
Table of contents
SQL INNER JOIN keyword (internal connection)
The internal link INNER JOIN keyword selects records with matching values in both tables.
SQL INNER JOIN syntax
SELECT column_name(s)
FROM table1
INNER JOIN table2 ON table1.column_name = table2.column_name;
Note: INNER JOIN is the same as JOIN.
Demonstrate the database
In this tutorial, we'll use the famous Northwind sample database.
Here's the data from the Customers table:
| CustomerID | CustomerName | ContactName | Address | City | PostalCode | Country |
|---|---|---|---|---|---|---|
|
1
|
Alfreds Futterkiste | Maria Anders | Obere Str. 57 | Berlin | 12209 | Germany |
| 2 | Ana Trujillo Emparedados y helados | Ana Trujillo | Avda. de la Constitución 2222 | México D.F. | 05021 | Mexico |
| 3 | Antonio Moreno Taquería | Antonio Moreno | Mataderos 2312 | México D.F. | 05023 | Mexico |
Data selected from the Orders table:
| OrderID | CustomerID | EmployeeID | OrderDate | ShipperID |
|---|---|---|---|---|
| 10308 | 2 | 7 | 1996-09-18 | 3 |
| 10309 | 37 | 3 | 1996-09-19 | 1 |
| 10310 | 77 | 8 | 1996-09-20 | 2 |
SQL INNER JOIN instance
The following SQL statement returns all customers who placed the order:
FROM Customers
INNER JOIN Orders
ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;
Note: If there is at least one match in the table, the INNER JOIN keyword returns a row. If the rows in the Customers table do not match Orders, the rows are not listed.
Add three tables
The following SQL statement selects all orders that contain customer and freight order information:
Code example:
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);