text: CREATE TABLE unused_table (id serial primary key);
  CREATE TABLE used_table (id serial primary key);
  
  CREATE TABLE vendors (
   vendor_code integer PRIMARY KEY,
   vendor_name character(35),
   vendor_city character(15),
   vendor_country character(20)
  );
  
  CREATE INDEX vendors_vendor_name_idx ON vendors (vendor_name);
  
  CREATE TABLE items (
   item_code integer,
   item_name character(35),
   purchase_unit character(10),
   sale_unit character(10),
   purchase_price numeric(10,2),
   sale_price numeric(10,2),
   PRIMARY KEY (item_code)
  );
  
  ALTER TABLE items ADD CONSTRAINT items_item_name_unique UNIQUE (item_name);
  
  CREATE TABLE orders (
   ord_no integer PRIMARY KEY,
   ord_date date,
   item_code integer,
   item_name character(35),
   item_grade character(1),
   ord_qty numeric,
   ord_amount numeric
  );
  ALTER TABLE orders ADD CONSTRAINT orders_items_item_code FOREIGN KEY (item_code) REFERENCES items(item_code);
  