1.Interviewer first asked about the projects in detail.He had discussion in everything the technologies used and why this project sort of questions.I had used MongoDB as database ,for which he said I will discuss later. I explained the architecture on the board. 2.Asked about DBMS ,SQL query,NULL values,how the NULL values are stored in SQL internal working in SQL. Asked about the SQL query for which I got little confused. Concept of foreign key.Can Foreign key be NULL.I said yes,asked the scenario where it can be done.Which table should be made referenced table and which referencing table. Can Unique key be NULL ,how many values can be made UNIQUE key NULL and why it can be done,the concept behind it. 3.Asked why I used MongoDB as database.Difference between SQL and NoSQL. 4.Questions related to C.If you know the basic and can only find the output rather than internal working ,it won't help ,How it is done internally and why,why not question in everything. questions in pointers. What is pointers? Why we make pointers of different datatypes? Relation between arrays and pointers. Malloc and calloc. Output question regarding this. Basic Data structures,which data structure is used types questions ? Asked what all technologies You have worked on,Asked in which field I am comfortable as they have different teams. From my side I got confused in answering SQL query for which he gave hint and one of the question. I am still figuring out where I missed.I think I said that I got bored by making app ,I like system programming,he was noting down what all things I know and in which I am interested,in which I have said OS and computer organisation. Key-Mostly focused on Database and C in detailed level.