027 SQL LEFT JOIN

Summary of the "SQL LEFT JOIN Keyword" page on W3Schools:

Purpose: The SQL LEFT JOIN keyword is used to return all records from the left table (table1), and the matched records from the right table (table2). If there are no matches in the right table, the result will contain NULL values for those columns.

Syntax:

SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

In some databases, LEFT JOIN can also be called LEFT OUTER JOIN.

Example: Using the Northwind sample database:
- The statement below lists all customers, and any orders they may have (customers with no orders will still appear, but with NULL for order columns):
```
SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
LEFT JOIN Orders
ON Customers.CustomerID = Orders.CustomerID
ORDER BY Customers.CustomerName;
```
Key Point: LEFT JOIN ensures every row from the left table appears in the results, even when there is no matching row in the right table.
Practice Exercise: The page offers a multiple-choice question to test understanding of the LEFT JOIN behavior.

This page is designed as a beginner-friendly tutorial with interactive and example features, ideal for quickly grasping the basics and syntax of SQL LEFT JOINs.

SQL LEFT JOIN Keyword

The LEFT JOIN keyword returns all records from the left table (table1), and the matching records from the right table (table2). The result is 0 records from the right side, if there is no match.

LEFT JOIN Syntax

SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

Note: In some databases LEFT JOIN is called LEFT OUTER JOIN.

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection 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

And a selection 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 LEFT JOIN Example

The following SQL statement will select all customers, and any orders they might have:

SELECT Customers.CustomerName, Orders.OrderID  
FROM Customers  
LEFT JOIN Orders ON Customers.CustomerID = Orders.CustomerID  
ORDER BY Customers.CustomerName;

Note: The LEFT JOIN keyword returns all records from the left table (Customers), even if there are no matches in the right table (Orders).