American Express Intenrship interview questions

I attended my schools' career fair and after the career fair, I got a phone call from American Express asking if I would like to do an interview. I accepted the interview and it was mainly technical questions.

I had to interview with 2 different people, each of them asked me a few technical questions and a few logical questions. The technical questions were about the difference between pass by value and pass by reference. What is a primary key.