Managing columns of table - oracle database script

-- Add column  alter table scott.emp add( empname varchar2(20)); alter table scott.emp add( empid number,deptid number);  -- Drop column  alter table scott.emp drop (empname); alter table scott.emp drop (empid,deptid);  -- Rename column  alter table scott.emp rename column empname to asocname;  -- set column unused  alter table scott.emp set unused (empname);  -- Drop unused columns from a table  alter table scott.emp drop unused columns.