title: Calculating the percentage across multiple columns
body: <p>Suppose I own a car racing company with a database that has information of all the races and racers. The database has a table for all of the racers (RacerID, first name, last name, contactInfo etc.) , and another table for all of the races (RaceID, racer1, racer1, winningRacerID, winningTime). </p>
  
  <p>How would you calculate the winning percentage of each racer?</p>