ERROR WITH DATABASE QUERY!

Query:
SELECT related_products.related_product_id AS related_id, products.part_name AS part_name FROM related_products, products WHERE related_products.product_id = AND related_products.related_product_id = products.product_id AND related_products.show_on_detail = "Y" ORDER BY `related_products`.`product_id` ASC

MySQL Error:
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AND related_products.related_product_id = products.product_id AND related_produc' at line 1