SQL left connection LEFT JOIN keyword

The SQL left link, the LEAF JOIN keyword, returns all the rows in the left table (Table 1), even if there is no match in the right table (Table 2). If there is no match in the correct table, the result is NULL.

SQL LEFT JOIN syntax 

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

Or: 

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

Note: In some databases, LEFT JOIN is called LEFT OUT ER JOIN.

SQL left connection LEFT JOIN keyword


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 LEFT JOIN instance

The following SQL statement will select all customers and any orders they may 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 rows in the left table (Customers), even if there is no match in the right table (Orders).