如何从数据库中显示类别和子类别

i need to fetch data from two tables one is category table and second is sub category table. In subcategory table i am saving primary key of category table. Now i need to fecth array from the table. first i want to show category name and its subcategories and then second category and its subcategory. This is my code to get category and subcategory list.i need to fetch data from two tables one is cat