| PRODUCTS | OPTIONS_PRODUCTS | OPTIONS | id <------. | option_id ---------> | id | name '- | product_id | name
しかしこの例ではうまくいきません
| PRODUCTS | OPTIONS_PRODUCTS | OPTIONS | id <------. | option_id ---------> | id | name '- | product_id | name | price # (Notice the difference) | price_level_id # (Or, to make things more complex...)