Can you please explain further what having equality on a field means?

Does a table have to have a primary key?

Could you explain how a primary key that requires multiple column values works?

How do we know when using JOIN is necessary?

Is using "join" the same as using "inner join"?

Could we also review one:many vs many:many mapping?
/ I'm still confused by the different mappings and how to implement each of them.

I'm confused about the representation of Many Many Relationships and when (in the given example) there are arrows coming from the movies to the 2 actors. 

I'm confused about the concept of many-to-many mapping. Using the actors-to-movies example, isn't each actor a unique individual? If that's the case, how can there be a many-to-many relationship between an actor and the movies they've appeared in, since there's only one actor for each movie they participate in?

Could intermediate tables be explained a bit more?

Can you give and explain an example of cross-product?

In the example with a pet table (primary key ""pid"") and an owner table (primary key ""oid""), I understand that the ""oid"" in the pet table is a foreign key that links each pet to its owner in the owner table, but I'm confused what happens to foreign keys when we merge these two tables?

I understand that the join operation is virtual and joining happens during a query and does not affect the representation of either table. However, does that mean that join does not create a separate table with the two tables merged? Or that it does, but after the query is executed, it does not save it anywhere?

Could you explain again the difference between JOIN and JOIN ON? 

In class, could you please go over natural joins again with more examples?

In what cases would it be helpful to use a natural join?

How does aliasing work with creating intermediate tables and what are its benefits?

How would you join more than two tables together?

I have a question on the "Join USING a shared field". You mention that we can join on fields that have the same name in two tables which makes sense. But in the future, say we have multiple tables that each may have many columns - is there an efficient way to keep track of the field names in each table? Or do we just have to call each table and see where the field names match up?

I think I am just a little confused overall but I think putting it into practice in class will help