text: drop procedure if exists product_list;
  delimiter //
  CREATE procedure product_list(cat varchar(50))
  begin
  	if upper(cat) in (select upper(category) from product) then
  		select * from Product where upper(Category)=upper(cat) and units_in_stock>0;
  	else
  		select * from Product where units_in_stock>0;
      end if;
  end //
  delimiter ;
  
  select * from product;
  call alter_product('furniture');
  select * from product;