Built this query, but any other suggestion is welcome'd.
Select Top 1000000 tblAssets.Username,
tblAssets.Userdomain,
Coalesce(tblADusers.Displayname, tblAssets.Username) As Displayname,
tblAssets.Lastseen,
tblAssets.AssetID,
tblAssets.AssetName,
tblADusers.OU,
tblADComputers.OU As OU1
From tblAssets
Inner Join tsysOS On tblAssets.OScode = tsysOS.OScode
Left Outer Join tblADusers On tblAssets.Userdomain = tblADusers.Userdomain And
tblAssets.Username = tblADusers.Username
Inner Join tblADComputers On tblAssets.AssetID = tblADComputers.AssetID
Order By tblAssets.Lastseen Desc