SQL LEFT JOIN Keyword

SQL LEFT JOIN Keyword

The LEFT JOIN keyword returns all rows from the left table (table_name1), even if there are no matching rows in the right table (table_name2).

LEFT JOIN Keyword Syntax

SELECT column_name(s)
FROM table_name1
LEFT JOIN table_name2
ON table_name1.column_name=table_name2.column_name

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

Original Table (used in the example):

"Persons" Table:

Id_P LastName FirstName Address City
1 Adams John Oxford Street London
2 Bush George Fifth Avenue New York
3 Carter Thomas Changan Street Beijing

"Orders" Table:

Id_O OrderNo Id_P
1 77895 3
2 44678 3
3 22456 1
4 24562 1
5 34764 65

LEFT JOIN (LEFT JOIN) Example

Now, we want to list all people, as well as their orders - if any.

You can use the following SELECT statement:

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
LEFT JOIN Orders
ON Persons.Id_P=Orders.Id_P
ORDER BY Persons.LastName

Result Set:

LastName FirstName OrderNo
Adams John 22456
Adams John 24562
Carter Thomas 77895
Carter Thomas 44678
Bush George 　

The LEFT JOIN keyword will return all rows from the left table (Persons), even if there are no matching rows in the right table (Orders).