Is there anything that can replace auto_increment?

What's the difference between saying relationships and relationship set or entities and entity set?

What do you mean by "set"  Is a relationship set a relationship (one line), or the set of multiple relationships in a diagram, or a set of the involved attributes...?  Similarly, is an entity set a single table, a set of all the items in a table, or a set of multiple tables?  

Can you show an in-class example with the ALTER TABLE syntax? I'm a little confused about how to use it. 

You mentioned that there can be only one director, but in some movies, there are actually two directors. How would we address this? I think we talked about this, but it might have slipped my mind...

I'm unsure how you enter data for the columns/tables in dbdiagram.io. Could we please go over that?

I don't understand how the two 1-many relationships translate to a many-to-many relationship, visually and intuitively? I understand how it works with the "<>" though.

I'm a little bit confused about ISA hierarchies. Could you explain what it does? / I would like to go over ISA structure in class.

How would you tell if two entities had an 'ISA' relationship  with multiple tables just by looking at the mysql code? Have we seen any examples of this in either the vet, wmdb, or movie_lens_db examples?

I'm still unsure about when it's best to handle an isa hierarchy via a large table vs. joins.