I think the author meant to say that the ID column is unique

his query is:

--Find duplicate records

--The result of this query is all the duplicate records whose Id is greater.

select a.* from Employees a

join Employees b on

a.[EmployeeNo] = b.[EmployeeNo]

AND a.[EmployeeID]= b.[EmployeeID]

AND a.Id>b.Id

so to delete records without creating a new table

delete * from employee where id NOT IN (select min(id) from employee group by employeeno, employeeid)

This will leave the min(id) for any duplicated record, correct?