设置别名变量

Question

我有来自SQL Server Management Studio 2005的以下T-SQL代码：

UPDATE O
SET DATAREVISIONTYPE = 'Modify', O.OriginalUserID = OriginalUserID, O.EmployeeBirthdate = EmployeeBirthdate, O.User_ID = User_ID
FROM LRN_Upload_Prep as O
WHERE DATAREVISIONTYPE = 'Add' AND
(SELECT COUNT([OriginalUserId]) FROM Lrn_Upload_Prep WHERE DataRevisionType = 'Transfer' AND FirstName = O.FirstName 
AND LastName = O.LastName AND EmployeeEmailAddress = O.EmployeeEmailAddress AND LEFT(EmployeeBirthdate, 4) = O.EmployeeBirthdate)> 0

我无法弄清楚如何使用别名修改SET中的数据（O.OriginalUserID = OriginalUserID，O.EmployeeBirthdate = EmployeeBirthdate，O.User_ID = User_ID），因为我的理解是别名尚未声明。我考虑将在CTE中声明别名的部分包裹起来，想想也许会起作用，但无济于事。对研究内容的任何修正或建议都很棒，谢谢！