SELECT
	rn = ROW_NUMBER() OVER (
		PARTITION BY Software_Name_Raw, Software_Version_Raw, Software_Publisher_Raw 
		ORDER BY Load_Date), 
	Software_Name_Raw,
	Software_Version_Raw,
	Software_Publisher_Raw,
	Software_Category,
	Software_Subcategory,
	MSDN_Flag,
	CDL_Flag,
	Source,
	Pending_Classification_Flag,
	Auto_Classification_Flag,
	Software_Classification_Version,
	Manual_Deletion,
	Load_Date
FROM lookuptable

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

SELECT DISTINCT col1, col2, col3
INTO lookuptable1
FROM lookuptable

CREATE TABLE lookuptable1
( ID int IDENTITY(1,1) PRIMARY KEY
, col1 nvarchar(50)
, col2 nvarchar(50)
, col3 nvarchar(50)
CONSTRAINT [uqLookuptable1cols1_3] UNIQUE (col1, col2, col3)
)

ALTER TABLE lookuptable1 ADD CONSTRAINT [uqLookuptable1cols1_3] UNIQUE (col1, col2, col3)