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 matches in the right table (table_name2).

SQL LEFT JOIN Syntax

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

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


SQL LEFT JOIN Example

The "Persons" table:

P_IdLastNameFirstNameAddressCity
1 Hansen Ola Timoteivn 10 Sandnes
2 Svendson Tove Borgvn 23 Sandnes
3 Pettersen Kari Storgt 20 Stavanger

The "Orders" table:

O_IdOrderNoP_Id
1 77895 3
2 44678 3
3 22456 1
4 24562 1
5 34764 15

Now we want to list all the persons and their orders - if any, from the tables above.

We use the following SELECT statement:

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

The result-set will look like this:

LastNameFirstNameOrderNo
Hansen Ola 22456
Hansen Ola 24562
Pettersen Kari 77895
Pettersen Kari 44678
Svendson Tove  

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