求一SQL语句：两次购买时间间隔

WITH ranked_transactions AS (
    SELECT
        user,
        date,
        ROW_NUMBER() OVER (
            PARTITION BY user
            ORDER BY date
        ) AS rn
    FROM transactions
)
SELECT
    t1.user,
    DATEDIFF(day, t1.date, t2.date) AS days_interval
FROM ranked_transactions t1
JOIN ranked_transactions t2
    ON t1.user = t2.user
    AND t1.rn = 1
    AND t2.rn = 2;