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Medical Center database
Non primary-foreign key JOINs
Non-equi JOINs
Non-equi self JOINs
25. Summary


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:
    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:
    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.


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