Q: How much does it cost to bake a cake?

Table Food
+----------+-------+
| Name     | Price |
+----------+-------+
| Cake     | 4     |
| Egg      | 8     |
| Frosting | 15    |
| Milk     | 16    |
| Sugar    | 23    |
+----------+-------+
(price does not include the cost of ingredients)


Table Recipe
+----------+------------+----------+
| Parent   | Ingredient | Quantity |
+----------+------------+----------+
| Cake     | Egg        | 8        |
| Cake     | Frosting   | 1        |
| Cake     | Milk       | 1        |
| Frosting | Egg        | 2        |
| Frosting | Milk       | 0.5      |
| Frosting | Sugar      | 3        |
+----------+------------+----------+

Goal: given the name of a food, determine its total cost including cost of ingredients.
Example 1: Frosting = (its own price) + 2 Egg + 1/2 Milk + 3 Sugar = 15 + 16 + 8 + 69 = 108$
Example 2: Cake = (its own price) + 8 Egg + 1 Frosting + 1 Milk = 4 + 64 + 108 + 16 = 192$

Notice that a nonrecursive solution can't calculate the total cost of cake, because you can't determine the total cost of Frosting that way.

Hard mode: cache the results of previous total cost calculations, so you don't have to e.g. re-query Eggs more than once.