Does primary key(aid,tid) mean the primary key is the value of both columns together?

Could you explain how Foreign keys are used in Referencial integrity? Where does the foreign key come from? Still abit confused on that part.

Could you please show an example in class on using indices to access specific column values?

How are indexes different from just using a primary key? / How are indexes better or different than a shared primary key?

What does index do exactly?

What is the difference between using a primary key versus another column (e.g., name) in an UPDATE statement?

Can we talk a little more about the usage of engine = InnoDB?

Can you build an index on multiple columns at a time or just one?

How do we determine which column we should use for building an index?

What does it mean by "allowing the integrity to be checked quickly"? / How exactly do indexes serve as a way to check referential integrity? 

Can you go over another simple example of referential integrity with a foreign key being a primary key in another table? 

Can we go over an example of importing from CSV to MySQL where one column is the primary key? 

What happens if the number of columns and the type of a table do not match the columns of the CSV file? Would we just get an error message?

Can you explain a bit more about what InnoDB is?

still a bit confused on innodb. is referential integrity one way or two way? still a bit confused on that too.