Zed-Axis Technologies interview questions

I got interview call letter through AMCAT. I was two day process. First they gave me a plain paper and 5 questions of SQL. It was a descriptive test ,there was not a single query . After that if your answeres were satisfying enough you'll said to wait for the technical interview. After tech interview you'll asked to leave for the day, if you are selected they'll contact you by mail or call. Some of questions that I remember are : 1. Write diff between primary key , foreign key, candidate key ? 2. What is joins in SQL and write their definitions and deferences between them? 3. How can we call a procedure from another procedure? 4. What is Self join?