Adding a large number of products to existing categories programmatically ( via php script)

We run a magento eshop and we would like to add a large number of products to existing categories programmatically ( via php script). All products data, like the product name, description, image url and category name etc., are already existing in a separately database. The name of the database is admin_fminer and table name is “product”. The table named “product” contains columns with all products' data. Column “level” contains the level of product’s category minus 2 and column g_parent contains the parent category of product's category. All categories are already imported in our eshop. So need to assign the products by categories in magento main database. Also needed the php source code in order to be used again in future update