/*quick script to show different results when
the join syntax is altered*/
USE [AdventureWorks]
GO

/*drop the tables if they already exist*/
IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[TableA]') AND type in (N'U'))
DROP TABLE [dbo].[TableA]
GO
IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[TableB]') AND type in (N'U'))
DROP TABLE [dbo].[TableB]
GO
IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[TableC]') AND type in (N'U'))
DROP TABLE [dbo].[TableC]
GO

/*create the tables, we only need the one column*/
CREATE TABLE [dbo].[TableA]([c1] [tinyint] NOT NULL) ON [PRIMARY]
GO
CREATE TABLE [dbo].[TableB]([c1] [tinyint] NOT NULL) ON [PRIMARY]
GO
CREATE TABLE [dbo].[TableC]([c1] [tinyint] NOT NULL) ON [PRIMARY]
GO

/*populate the tables with some values, we don't need many. in fact
we only need to have one value represent each of the seven
possible regions in the 3-circle overlapping Venn diagram*/
SET NOCOUNT ON
INSERT INTO [dbo].[TableA] ([c1]) VALUES (1)
INSERT INTO [dbo].[TableA] ([c1]) VALUES (2)
INSERT INTO [dbo].[TableA] ([c1]) VALUES (3)
INSERT INTO [dbo].[TableA] ([c1]) VALUES (5)
INSERT INTO [dbo].[TableB] ([c1]) VALUES (1)
INSERT INTO [dbo].[TableB] ([c1]) VALUES (3)
INSERT INTO [dbo].[TableB] ([c1]) VALUES (4)
INSERT INTO [dbo].[TableB] ([c1]) VALUES (6)
INSERT INTO [dbo].[TableC] ([c1]) VALUES (1)
INSERT INTO [dbo].[TableC] ([c1]) VALUES (2)
INSERT INTO [dbo].[TableC] ([c1]) VALUES (4)
INSERT INTO [dbo].[TableC] ([c1]) VALUES (7)
GO

/*ok, here is the magic, let's do a join using A.c1 twice
and examine the four rows returned*/
SELECT A.c1 as [A_val], B.c1 as [B_val], C.c1 as [C_val]
FROM TableA A LEFT JOIN TableB B ON A.c1 = B.c1
LEFT JOIN TableC C ON A.c1 = C.c1

/*ok, let's change this to using B.c1*/
SELECT A.c1 as [A_val], B.c1 as [B_val], C.c1 as [C_val]
FROM TableA A LEFT JOIN TableB B ON A.c1 = B.c1
LEFT JOIN TableC C ON B.c1 = C.c1

/*See the difference in the results? The values in the C_val column
are different depending on what you use for the join key.

So if you were only looking at the C_val column in your select list
you would be getting different results and you might not understand
why, which can be a source of frustration for many as they try
to get the right data returned.*/