When are ER diagrams used in real life problems?

Could we please go over keys and key constraints in class?

Can we go over the definition of a foreign key constraint again?

Are there limits on how many intermediate tables we can have?

Can you explain intermediate tables with an example?

Is there a limit to the number of relationships between entities? 

What is the best practice when understanding each of the different relationships so we don't get them all mixed up?

Do you mind going over entity & entity set vs relationship & relationship set? / Can you go over relationship set vs entity set? / What exactly is the difference between relations and relationships as mentioned in Q2 in the quiz? 

I would like to practice more with creating ER diagrams in class.

Is there a way to create multiple many-many relationships in dbdiagram? Is it recommended to do so?

Can you go over ISA hierarchies in class I'm still a little confused. / Could you go over ISA hierarchies / Can you explain a bit more about ISA hierarchies?

Are subtypes also entities?

Can ALTER TABLE change overall table structure/layout?

Can we go over the Alter Table syntax?

Are we supposed to make a diagram first and then work on the code we export from dbdiagram? Or what do we do with the code we downloaded.