1. Imagine a table keeping track of all the rides a driver undertakes in a given day. How do you query that table to find out the time when he did not have any rides. So the table may have a record when he picks up his first ride and then he picks another and then drops both of them. After a while he picks up a few more which again is recorded in the table. So with all that how do you find the data when he does not have any rides