Creating existing column identity in existing table

Hi friends ,

Suppose i have one table " shipmentpincode " , which have following columns :-

 I want to make Id column of this table identity . Then i have to fulfill following steps : -

• First , create a temp column in table 

Alter Table shipmentpincode Add Id_new int Identity(1, 1) not null primary key 

Go

• Second, drop existing column 

Alter Table shipmentpincode Drop Column Id

Go

• Rename new column to old column name 

  Exec sp_rename 'shipmentpincode.Id_new', 'Id', 'Column'