1. Oracle : SQL

4. ALTER TABLE tablename ADD (column name datatype [DEFAULT expression],
e.g. ALTER TABLE copy_f_staffs
ADD (hire_date DATE DEFAULT SYSDATE)
MODIFY (column name datatype [DEFAULT expression],
column name datatype, ...
MODIFY (hire_date DATE)
DROP COLUMN column name;
DROP COLUMN manager_target;

5. DROP UNUSED (manager_budget)
ALTER TABLE tablename
DROP COLUMN column name;
e.g. ALTER TABLE copy_f_staffs
DROP COLUMN manager_target;
SET UNUSED (column name);
SET UNUSED (manager_budget);
DROP UNUSED COLUMNS;
DROP UNUSED (manager_budget)

6. RENAME old_name to new_name;
DROP TABLE tablename;
e.g. DROP TABLE copy_f_staffs;
RENAME old_name to new_name;
e.g. RENAME copy_f_staffs to copy_fastfood_staffs;
TRUNCATE TABLE tablename:
COMMENT ON TABLE tablename | COLUMN table.column
IS 'place your comment here';
e.g. COMMENT ON TABLE employees
IS 'the employee table if for the Western Region only';
If you want to drop a comment previously made on a table or column, use the empty string ( ' ' );
IS ' ' ;