มีรหัสจักรยานที่แตกต่างกันกี่รหัส?ไม่จำเป็นต้องใช้ตารางทั้งหมด
How many different bike ids are there?It is not neccessary to use all the tables.
 weather:  date [ text]  max_temperature_f [ number]  mean_temperature_f [ number]  min_temperature_f [ number]  max_dew_point_f [ number]  mean_dew_point_f [ number]  min_dew_point_f [ number]  max_humidity [ number]  mean_humidity [ number]  min_humidity [ number]  max_sea_level_pressure_inches [ number]  mean_sea_level_pressure_inches [ number]  min_sea_level_pressure_inches [ number]  max_visibility_miles [ number]  mean_visibility_miles [ number]  min_visibility_miles [ number]  max_wind_speed_mph [ number]  mean_wind_speed_mph [ number]  max_gust_speed_mph [ number]  precipitation_inches [ number]  cloud_cover [ number]  events [ text]  wind_dir_degrees [ number]  zip_code [ number] 
SELECT COUNT(DISTINCT bike_id) FROM trip