I recently came up with a problem which I would like to share some thoughts about with someone on this forum. This relates to finding a subset. In reality it is more complicated, but I tried to present it here using some simpler concepts. To make things easier, I created this conceptual DB model: Let's assume this is a DB for storing recipes. Recipe can have many instructions steps and many ingredients. Ingredients are stored in a cupboard and we know how much of each ingredient we have. Now, when we create a recipe, we have to define how much of each ingredient we need. When we want to use a recipe, we would just check if required amount is less than available amount for each product and then decide if we can cook a dinner - if amount required for at least one ingredient is less than available amount - recipe cannot be cooked. Simple sql query to get the result. This is straightforward, but I'm wondering, how should I work when the problem is stated the other way round, i.e. how to find recipies which can be cooked only from ingredients that are available? I hope my explanation is clear, but if you need any more clarification, please ask.