Meta Data Scientist interview questions

I had interviewed with Facebook for university grad data scientist position. I couldn't clear the SQL round and got rejected. I had got an email from the recruiter and was asked to fill some questions. After I completed that a 15 mins round with HR was scheduled. He asked me some SQL questions and one hypothetical case regarding my favorite facebook product. (Don't take this round very lightly I have heard people getting rejected from this round as well). After that round, I was scheduled a skype round with the Data Science Manager which was divided into SQL query and product based questions. He gave me SQL queries to write, my queries were perfect but I didn't write an optimize query which was the problem. Don't write big queries try to write optimized queries. The product related questions were quite straight forward and I don't think they are looking for specific answers. So one can just practice some questions like how will you test the success of a product? Or What changes will you propose to make the product better, etc. I was asked the usage of the status updates has decreased so how will you test that thing? Overall I believe the SQL query should be really good to clear this round.