sql masukkan ke dalam tabel dengan nilai kasus tertentu

Anda perlu koma setelah end menyelesaikan pernyataan kasus. Dan, "sebagai" diletakkan setelah case pernyataan, bukan di dalamnya:

Insert into TblStuff(FullName, Address, City, Zip)
    Select (Case When Middle is Null Then Fname + LName
                 Else Fname +' ' + Middle + ' '+ Lname
            End)  as FullName,
           (Case When Address2 is Null Then Address1
                 else Address1 +', ' + Address2
            End)  as  Address,
           City as City,
           Zip as Zip
    from tblImport