Quiz

1. I am a little confused about how foreign keys work, especially in many to many joins.

   Sure; that is confusing. Lots of people have trouble at first.

   I like to think of them a pairs, as in actor P was in movie M, so (P,M) is in the credits (acting credits) table.

   Example: P=Emma Watson, and M="Harry Potter and the Sorcerer's Stone", we add that pair to the credits table.

   Or rather, we add their keys to that table: (nm0914612,tt0241527)

   If there's additional information about that pair, we can add it to that table.

   Example: P=Emma Watson, and M=Harry Potter, we could add the role, R="Hermione Granger" or her salary or ...

   Consider: there's no place for that information in either Emma Watson's entry, nor in the movie's entry: no lists of data.

2. could you go more into the pros and cons of relational vs. non-relational databases?

   I just tried to, but here's a summary:

   • NoSQL: no fixed structure
   • SQL: data integrity
   • NoSQ: horizontal scaling
   • SQL: decades of experience