SELECT 
    N_WEEK as week_number,
    COUNT(TICKET_NO) as ticket_amount,
    festival_week,
    festival_name

FROM
    (
    SELECT 
    ticket_no,
    flight_id,
    n_week

    FROM 
    ticket_flights LEFT JOIN (
        SELECT
        flight_id as flight_ids,
        EXTRACT(WEEK FROM arrival_time) as n_week
        FROM flights
        WHERE
        arrival_airport IN (SELECT airport_code
                            FROM airports
                            WHERE city = 'Москва')
        AND arrival_time BETWEEN '2018-07-23' AND '2018-09-30') 
    AS msc_fly ON ticket_flights.flight_id = msc_fly.flight_ids
    
    ) as msc_ticket_flights
LEFT JOIN
    (
    SELECT
    festival_name,
    EXTRACT(WEEK FROM festival_date) as festival_week
    FROM festivals
    WHERE festival_city = 'Москва'
    ) as msc_festivals
ON msc_ticket_flights.n_week = msc_festivals.festival_week
WHERE n_week IS NOT NULL

GROUP BY week_number, festival_week, festival_name