Schema:
CREATE TABLE time_interval (
    period text,
    begin_time int,
    end_time int
)

CREATE TABLE flight_leg (
    flight_id int,
    leg_number int,
    leg_flight int
)

CREATE TABLE airline (
    airline_code varchar,
    airline_name text,
    note text
)

CREATE TABLE ground_service (
    city_code text,
    airport_code text,
    transport_type text,
    ground_fare int
)

CREATE TABLE class_of_service (
    booking_class varchar,
    rank int,
    class_description text
)

CREATE TABLE restriction (
    restriction_code text,
    advance_purchase int,
    stopovers text,
    saturday_stay_required text,
    minimum_stay int,
    maximum_stay int,
    application text,
    no_discounts text
)

CREATE TABLE date_day (
    month_number int,
    day_number int,
    year int,
    day_name varchar
)

CREATE TABLE dual_carrier (
    main_airline varchar,
    low_flight_number int,
    high_flight_number int,
    dual_airline varchar,
    service_name text
)

CREATE TABLE compartment_class (
    compartment varchar,
    class_type varchar
)

CREATE TABLE equipment_sequence (
    aircraft_code_sequence varchar,
    aircraft_code varchar
)

CREATE TABLE flight (
    aircraft_code_sequence text,
    airline_code varchar,
    airline_flight text,
    arrival_time int,
    connections int,
    departure_time int,
    dual_carrier text,
    flight_days text,
    flight_id int,
    flight_number int,
    from_airport varchar,
    meal_code text,
    stops int,
    time_elapsed int,
    to_airport varchar
)

CREATE TABLE month (
    month_number int,
    month_name text
)

CREATE TABLE code_description (
    code varchar,
    description text
)

CREATE TABLE airport (
    airport_code varchar,
    airport_name text,
    airport_location text,
    state_code varchar,
    country_name varchar,
    time_zone_code varchar,
    minimum_connect_time int
)

CREATE TABLE state (
    state_code text,
    state_name text,
    country_name text
)

CREATE TABLE food_service (
    meal_code text,
    meal_number int,
    compartment text,
    meal_description varchar
)

CREATE TABLE city (
    city_code varchar,
    city_name varchar,
    state_code varchar,
    country_name varchar,
    time_zone_code varchar
)

CREATE TABLE time_zone (
    time_zone_code text,
    time_zone_name text,
    hours_from_gmt int
)

CREATE TABLE flight_stop (
    flight_id int,
    stop_number int,
    stop_days text,
    stop_airport text,
    arrival_time int,
    arrival_airline text,
    arrival_flight_number int,
    departure_time int,
    departure_airline text,
    departure_flight_number int,
    stop_time int
)

CREATE TABLE flight_fare (
    flight_id int,
    fare_id int
)

CREATE TABLE days (
    days_code varchar,
    day_name varchar
)

CREATE TABLE fare_basis (
    fare_basis_code text,
    booking_class text,
    class_type text,
    premium text,
    economy text,
    discounted text,
    night text,
    season text,
    basis_days text
)

CREATE TABLE fare (
    fare_id int,
    from_airport varchar,
    to_airport varchar,
    fare_basis_code text,
    fare_airline text,
    restriction_code text,
    one_direction_cost int,
    round_trip_cost int,
    round_trip_required varchar
)

CREATE TABLE aircraft (
    aircraft_code varchar,
    aircraft_description varchar,
    manufacturer varchar,
    basic_type varchar,
    engines int,
    propulsion varchar,
    wide_body varchar,
    wing_span int,
    length int,
    weight int,
    capacity int,
    pay_load int,
    cruising_speed int,
    range_miles int,
    pressurized varchar
)

CREATE TABLE airport_service (
    city_code varchar,
    airport_code varchar,
    miles_distant int,
    direction varchar,
    minutes_distant int
)

Question: what are the early morning flights from BOSTON to DENVER

SQL:
SELECT DISTINCT flight.flight_id FROM airport_service AS AIRPORT_SERVICE_0, airport_service AS AIRPORT_SERVICE_1, city AS CITY_0, city AS CITY_1, flight WHERE (CITY_0.city_code = AIRPORT_SERVICE_0.city_code AND CITY_0.city_name = 'BOSTON' AND CITY_1.city_code = AIRPORT_SERVICE_1.city_code AND CITY_1.city_name = 'DENVER' AND flight.from_airport = AIRPORT_SERVICE_0.airport_code AND flight.to_airport = AIRPORT_SERVICE_1.airport_code) AND flight.departure_time BETWEEN 0 AND 800