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_Id | LastName | FirstName | Address | City |
---|---|---|---|---|
1 | Hansen | Ola | Timoteivn 10 | Sandnes |
2 | Svendson | Tove | Borgvn 23 | Sandnes |
3 | Pettersen | Kari | Storgt 20 | Stavanger |
The "Orders" table:
O_Id | OrderNo | P_Id |
---|---|---|
1 | 77895 | 3 |
2 | 44678 | 3 |
3 | 22456 | 1 |
4 | 24562 | 1 |
5 | 34764 | 15 |
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:
LastName | FirstName | OrderNo |
---|---|---|
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).
SQL LEFT JOIN Keyword
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