title: how can I add new column with substract other two existing column to have the values in bigquery
body: <p>ride_id STRING  NULLABLE<br />
  rideable_type   STRING  NULLABLE<br />
  started_at  TIMESTAMP   NULLABLE<br />
  ended_at    TIMESTAMP   NULLABLE<br />
  start_station_name  STRING  NULLABLE<br />
  start_station_id    INTEGER NULLABLE<br />
  end_station_name    STRING  NULLABLE<br />
  end_station_id  INTEGER NULLABLE<br />
  start_lat   FLOAT   NULLABLE<br />
  start_lng   FLOAT   NULLABLE<br />
  end_lat FLOAT   NULLABLE<br />
  end_lng FLOAT   NULLABLE<br />
  member_casual   STRING  NULLABLE<br />
  ride_length</p>