Alright! Let's summarize everything we learned in this part.

• We don't have to join tables on the primary-foreign key relationship. It is possible to use any two columns:

  SELECT
    buyer.name,
    car.name
  FROM buyer
  JOIN car
    ON owner.preferred_car_type = car.type
  

  The query above will show the name of every buyer together with every car that matches their preferred type.
• We also don't have to use the equality operator when joining tables. We are free to use other comparison operators (<, >, <=, >=, !=, <>) or the BETWEEN operator:

  SELECT
    auctioneer.name,
    item.name
  FROM auctioneer
  JOIN item
    ON auctioneer.funds > item.price
  

• We can write a special kind of JOIN to list items within a certain range (for example, within a budget), all pairs of items, or all unique pairs.