table

I am coping a standard table into a new table in 9.1 release. I am trying to add a column that already exists. For example there is a column called with dd item doco however I want to add another doco but the system doesnt allow. Another question is if I can remane a column. For example i have a column dcto with column name as order type. I want to remane order type to something else and want to know if I can do that.