Example
This will get all the orders for all customers:
SELECT c.CustomerName, o.OrderID
FROM Customers AS c
INNER JOIN Orders AS o
ON c.CustomerID = o.CustomerID
ORDER BY c.CustomerName, o.OrderID;
This will count the number of orders for each customer:
SELECT c.CustomerName, COUNT(*) AS 'Order Count'
FROM Customers AS c
INNER JOIN Orders AS o
ON c.CustomerID = o.CustomerID
GROUP BY c.CustomerID;
ORDER BY c.CustomerName;
Also, counts, but probably faster:
SELECT c.CustomerName,
( SELECT COUNT(*) FROM Orders WHERE CustomerID = c.CustomerID ) AS 'Order Count'
FROM Customers AS c
ORDER BY c.CustomerName;
List only the customer with orders.
SELECT c.CustomerName,
FROM Customers AS c
WHERE EXISTS ( SELECT * FROM Orders WHERE CustomerID = c.CustomerID )
ORDER BY c.CustomerName;
