You are now a sqlite data analyst, and you are given a database schema as follows:

    【Schema】
    【DB_ID】 formula_1
【Schema】
# Table: drivers
[
(driverId:INTEGER, Primary Key, Examples: [452, 625, 103]),
(driverRef:TEXT, Examples: [hamilton, heidfeld, rosberg]),
(number:INTEGER, Examples: [44, 6, 14]),
(code:TEXT, Examples: [HAM, HEI, ROS]),
(forename:TEXT, Examples: [Lewis, Nick, Nico]),
(surname:TEXT, Examples: [Hamilton, Heidfeld, Rosberg]),
(dob:DATE, Examples: [1985-01-07]),
(nationality:TEXT, Examples: [British, German, Spanish]),
(url:TEXT)
]
# Table: seasons
[
(year:INTEGER, Primary Key, Examples: [1950, 1951, 1952]),
(url:TEXT)
]
# Table: lapTimes
[
(raceId:INTEGER, Primary Key, Examples: [1, 2, 3]),
(driverId:INTEGER, Primary Key, Examples: [1, 2, 3]),
(lap:INTEGER, Primary Key, Examples: [1, 2, 3]),
(position:INTEGER, Examples: [13, 12, 11]),
(time:TEXT, Examples: [1:49.088, 1:33.740, 1:31.600]),
(milliseconds:INTEGER, Examples: [109088, 93740, 91600])
]
# Table: status
[
(statusId:INTEGER, Primary Key, Examples: [1, 2, 3]),
(status:TEXT, Examples: [Finished, Disqualified, Accident])
]
# Table: constructors
[
(constructorId:INTEGER, Primary Key, Examples: [147, 39, 54]),
(constructorRef:TEXT, Examples: [mclaren, bmw_sauber, williams]),
(name:TEXT, Examples: [AFM, AGS, ATS]),
(nationality:TEXT, Examples: [British, German, French]),
(url:TEXT)
]
# Table: pitStops
[
(raceId:INTEGER, Primary Key, Examples: [841, 842, 843]),
(driverId:INTEGER, Primary Key, Examples: [1, 2, 3]),
(stop:INTEGER, Primary Key, Examples: [1, 2, 3]),
(lap:INTEGER, Examples: [16, 36, 15]),
(time:TEXT, Examples: [17:28:24, 17:59:29, 17:27:41]),
(duration:TEXT, Examples: [23.227, 23.199, 22.994]),
(milliseconds:INTEGER, Examples: [23227, 23199, 22994])
]
# Table: qualifying
[
(qualifyId:INTEGER, Primary Key, Examples: [1, 2, 3]),
(raceId:INTEGER, Examples: [18, 19, 20]),
(driverId:INTEGER, Examples: [1, 9, 5]),
(constructorId:INTEGER, Examples: [1, 2, 6]),
(number:INTEGER, Examples: [22, 4, 23]),
(position:INTEGER, Examples: [1, 2, 3]),
(q1:TEXT, Examples: [1:26.572, 1:26.103, 1:25.664]),
(q2:TEXT, Examples: [1:25.187, 1:25.315, 1:25.452]),
(q3:TEXT, Examples: [1:26.714, 1:26.869, 1:27.079])
]
# Table: races
[
(raceId:INTEGER, Primary Key, Examples: [837, 833, 838]),
(year:INTEGER, Examples: [2009, 2008, 2007]),
(round:INTEGER, Examples: [1, 2, 3]),
(circuitId:INTEGER, Examples: [1, 2, 17]),
(name:TEXT, Examples: [Australian Grand Prix]),
(date:DATE, Examples: [2009-03-29]),
(time:TEXT, Examples: [06:00:00, 09:00:00, 07:00:00]),
(url:TEXT)
]
# Table: results
[
(resultId:INTEGER, Primary Key, Examples: [1, 2, 3]),
(raceId:INTEGER, Examples: [18, 19, 20]),
(driverId:INTEGER, Examples: [1, 2, 3]),
(constructorId:INTEGER, Examples: [1, 2, 3]),
(number:INTEGER, Examples: [22, 3, 7]),
(grid:INTEGER, Examples: [1, 5, 7]),
(position:INTEGER, Examples: [1, 2, 3]),
(positionText:TEXT, Examples: [1, 2, 3]),
(positionOrder:INTEGER, Examples: [1, 2, 3]),
(points:REAL, Examples: [10.0, 8.0, 6.0]),
(laps:INTEGER, Examples: [58, 57, 55]),
(time:TEXT, Examples: [1:34:50.616, +5.478, +8.163]),
(milliseconds:INTEGER, Examples: [5690616, 5696094, 5698779]),
(fastestLap:INTEGER, Examples: [39, 41, 58]),
(rank:INTEGER, Examples: [2, 3, 5]),
(fastestLapTime:TEXT, Examples: [1:27.452, 1:27.739, 1:28.090]),
(fastestLapSpeed:TEXT, Examples: [218.300, 217.586, 216.719]),
(statusId:INTEGER, Examples: [1, 11, 5])
]
# Table: constructorStandings
[
(constructorStandingsId:INTEGER, Primary Key, Examples: [1, 2, 3]),
(raceId:INTEGER, Examples: [18, 19, 20]),
(constructorId:INTEGER, Examples: [1, 2, 3]),
(points:REAL, Examples: [14.0, 8.0, 9.0]),
(position:INTEGER, Examples: [1, 3, 2]),
(positionText:TEXT, Examples: [1, 3, 2]),
(wins:INTEGER, Examples: [1, 0, 2])
]
# Table: driverStandings
[
(driverStandingsId:INTEGER, Primary Key, Examples: [1, 2, 3]),
(raceId:INTEGER, Examples: [18, 19, 20]),
(driverId:INTEGER, Examples: [1, 2, 3]),
(points:REAL, Examples: [10.0, 8.0, 6.0]),
(position:INTEGER, Examples: [1, 2, 3]),
(positionText:TEXT, Examples: [1, 2, 3]),
(wins:INTEGER, Examples: [1, 0, 2])
]
# Table: circuits
[
(circuitId:INTEGER, Primary Key, Examples: [23, 61, 29]),
(circuitRef:TEXT, Examples: [sepang, bahrain, catalunya]),
(name:TEXT, Examples: [Sepang International Circuit]),
(location:TEXT, Examples: [Kuala Lumpur, Sakhir, Montmeló]),
(country:TEXT, Examples: [Malaysia, Bahrain, Spain]),
(lat:REAL, Examples: [2.76083, 26.0325, 41.57]),
(lng:REAL, Examples: [101.738, 50.5106, 2.26111]),
(alt:INTEGER),
(url:TEXT)
]
# Table: constructorResults
[
(constructorResultsId:INTEGER, Primary Key, Examples: [1, 2, 3]),
(raceId:INTEGER, Examples: [18, 19, 20]),
(constructorId:INTEGER, Examples: [1, 2, 3]),
(points:REAL, Examples: [14.0, 8.0, 9.0]),
(status:TEXT, Examples: [D])
]
【Foreign keys】
lapTimes.raceId=races.raceId
lapTimes.driverId=drivers.driverId
pitStops.raceId=races.raceId
pitStops.driverId=drivers.driverId
qualifying.raceId=races.raceId
qualifying.driverId=drivers.driverId
qualifying.constructorId=constructors.constructorId
races.year=seasons.year
races.circuitId=circuits.circuitId
results.raceId=races.raceId
results.driverId=drivers.driverId
results.constructorId=constructors.constructorId
results.statusId=status.statusId
constructorStandings.raceId=races.raceId
constructorStandings.constructorId=constructors.constructorId
driverStandings.raceId=races.raceId
driverStandings.driverId=drivers.driverId
constructorResults.raceId=races.raceId
constructorResults.constructorId=constructors.constructorId

    【Question】
    How many drivers don't have a code? don't have a code refers to code is null

    【Evidence】
    don't have a code refers to code is null

    Please read and understand the database schema carefully, and generate an executable SQL based on the user's question and evidence. 

SQL: SELECT COUNT(driverId) - COUNT(CASE WHEN code IS NOT NULL THEN code END) FROM drivers