a. The difference in start_date vs today ( I am able to achieve this using datediff function)
b. I want to apply group by to 'id' column and take the latest date in the start_date column. In the above example for id=1 and start_date = 2018/06/05. Once I am able to group by id and get the latest start_date for that id then I would find diff of it with today's date.