Расш. возм. SQL. Урок 7. Подзапросы. задача 4/4

SELECT
    EXTRACT (week FROM subq.trunc_date) AS week_number,
    AVG(subq.transaction_per_day) AS avg_week_transaction
FROM
    (SELECT
        COUNT(DISTINCT id_transaction) AS transaction_per_day,
        DATE_TRUNC('day', DATE) AS trunc_date
    FROM
        transactions
    GROUP BY
        trunc_date) AS subq;
GROUP BY
   week_number