Shows how to select COUNT and SUM of the contents of certain columns. Line 1 selects columns from the Customers table, as well as the COUNT of the orders in the OrderID column of the Orders table, and the SUM of the Price column from the Orders table. Line 5 groups everything by Customer ID. The result is that you get a line for each CustomerID with the LastName and FirstName, as well as a COUNT of all of that customer's orders, and a SUM of the value of all of the customers orders.
SELECT Customers.CustomerID, Customers.LastName, Customers.FirstName, COUNT(Orders.OrderID) AS 'No. of Orders', SUM(Orders.Price) AS 'Total of Purchases' FROM Customers INNER JOIN Orders ON Customers.CustomerID=Orders.CustomerID GROUP BY Orders.CustomerID; -- You can count the rows in a table by using COUNT(1) SELECT COUNT(1) AS 'Number of Rows in Customers Table' FROM Customers