SQLJOIN Keyword
INNER JOIN
TheINNER JOIN command returns rows that have matching values in both tables.
The following SQL selects all orders with customer information:
Example
FROM Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;
Note: The INNER JOIN keyword selects all rows from both tables as long as there is a match between the columns. If there are records in the "Orders" table that do not have matches in "Customers", these orders will not be shown!
The following SQL statement selects all orders with customer and shipper information:
Example
FROM ((Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID)
INNER JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID);
LEFT JOIN
TheLEFT JOIN command returns all rows from the left table, and the matching rows from the right table. The result is NULL from the right side, if there is no match.
The following SQL will select all customers, and any orders they might have:
Example
FROM Customers
LEFT JOIN Orders ON Customers.CustomerID = Orders.CustomerID
ORDER BY Customers.CustomerName;
Note: TheLEFT JOIN keyword returns all records from the left table (Customers), even if there are no matches in the right table (Orders).
RIGHT JOIN
TheRIGHT JOIN command returns all rows from the right table, and the matching records from the left table. The result is NULL from the left side, when there is no match.
The following SQL will return all employees, and any orders they might have placed:
Example
FROM Orders
RIGHT JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID
ORDER BY Orders.OrderID;
Note: TheRIGHT JOIN keyword returns all records from the right table (Employees), even if there are no matches in the left table (Orders).
FULL OUTER JOIN
TheFULL OUTER JOIN command returns all rows when there is a match in either left table or right table.
The following SQL statement selects all customers, and all orders:
FROM Customers
FULL OUTER JOIN OrdersON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;
Note: TheFULL OUTER JOIN keyword returns all the rows from the left table (Customers), and all the rows from the right table (Orders). If there are rows in "Customers" that do not have matches in "Orders", or if there are rows in "Orders" that do not have matches in "Customers", those rows will be listed as well.
