SQL Server Error Messages - Msg 104
    Error Message
    Server: Msg 104, Level 15, State 1, Line 1
ORDER BY items must appear in the select list if the statement contains a UNION operator.
    Causes
	This error happens when you are using the UNION operator when combining the 
		results of multiple SELECT statements and you also specified an ORDER BY clause 
		where the columns in the ORDER BY clause are not part of the columns in your 
		SELECT list.
                    
    To illustrate, suppose you have 2 tables that contain the employees and managers 
	in a company. Both tables have a FirstName and LastName columns and you want to 
	generate a list of these names where the first name and last name are 
	concatenated together to form the full name and sort the output by the LastName 
	column:
												SELECT [FirstName] + [LastName] AS [FullName]
FROM [dbo].[Employees]
UNION
SELECT [FirstName] + [LastName] AS [FullName]
FROM [dbo].[Managers]
ORDER BY [LastName]
	Since the LastName column is not part of the output, although it’s part of one 
		of the columns in the SELECT list, the following error will be encountered:
	Server: Msg 104, Level 15, State 1, Line 3
ORDER BY items must appear in the select list if the statement contains a UNION operator.