SQL JOIN 3 Tables

Problem: List all suppliers with products that have sold, sorted by supplier.

SELECT DISTINCT CompanyName, ProductName
  FROM Supplier S
  JOIN Product P ON S.Id = P.SupplierId
  JOIN OrderItem I ON P.Id = I.ProductId
 ORDER BY CompanyName

Note: This query returns 77 records.
Removing the second JOIN returns 78 records, because only 1 product never sold.

CompanyName	ProductName
Aux joyeux ecclésiastiques	Chartreuse verte
Aux joyeux ecclésiastiques	Côte de Blaye
Bigfoot Breweries	Laughing Lumberjack Lager
Bigfoot Breweries	Sasquatch Ale
Bigfoot Breweries	Steeleye Stout
Cooperativa de Quesos 'Las Cabras'	Queso Cabrales

3-Table JOIN syntax.

SELECT column-names
  FROM table-name1 
  JOIN table-name2 ON column-name1 = column-name2
  JOIN table-name3 ON column-name3 = column-name4
 WHERE condition

3-Table INNER JOIN syntax.

SELECT column-names
  FROM table-name1 
 INNER JOIN table-name2 ON column-name1 = column-name2
 INNER JOIN table-name3 ON column-name3 = column-name4
 WHERE condition

The INNER keyword is optional.
INNER JOINs are the most commonly used type of JOIN.

SELECT O.OrderNumber, CONVERT(date,O.OrderDate) AS Date, 
       P.ProductName, I.Quantity, I.UnitPrice 
  FROM [Order] O 
  JOIN OrderItem I ON O.Id = I.OrderId 
  JOIN Product P ON P.Id = I.ProductId
 ORDER BY O.OrderNumber

This query performs 2 JOIN operations with 3 tables.
O, I, and P are table aliases. Date is a column alias.

OrderNumber	Date	ProductName	Quantity	UnitPrice
542378	7/4/2012	Queso Cabrales	12	14.00
542378	7/4/2012	Singaporean Hokkien Fried Mee	10	9.80
542378	7/4/2012	Mozzarella di Giovanni	5	34.80
542379	7/5/2012	Tofu	9	18.60
542379	7/5/2012	Manjimup Dried Apples	40	42.40
542380	7/8/2012	Jack's New England Clam Chowder	10	7.70
542380	7/8/2012	Manjimup Dried Apples	35	42.40
542380	7/8/2012	Louisiana Fiery Hot Pepper Sauce	15	16.80
542381	7/8/2012	Gustaf's Knäckebröd	6	16.80
542381	7/8/2012	Ravioli Angelo	15	15.60
542381	7/8/2012	Louisiana Fiery Hot Pepper Sauce	20	16.80
542382	7/9/2012	Sir Rodney's Marmalade	40	64.80
542382	7/9/2012	Geitost	25	2.00

• Our Sql LEFT JOIN Tutorial
• Our Sql RIGHT JOIN Tutorial
• Our Sql JOIN Multiple Tables Tutorial