The SQL Round

WITH ranked AS (
  SELECT
    *,
    ROW_NUMBER() OVER (
      PARTITION BY user_id
      ORDER BY event_timestamp DESC, event_id DESC
    ) AS rn
  FROM event_data
)
SELECT user_id, event_timestamp, event_id, payload
FROM ranked
WHERE rn = 1;

WITH daily AS (
  SELECT DISTINCT user_id, substr(event_timestamp, 1, 10) AS event_date
  FROM event_data
),
grouped AS (
  SELECT
    user_id,
    event_date,
    julianday(event_date) -
      ROW_NUMBER() OVER (PARTITION BY user_id ORDER BY event_date)
      AS streak_key
  FROM daily
)
SELECT user_id, MIN(event_date) AS streak_start, COUNT(*) AS streak_days
FROM grouped
GROUP BY user_id, streak_key
HAVING COUNT(*) >= 3;

WITH daily_revenue_summary AS (
  SELECT
    substr(transaction_date, 1, 10) AS order_date,
    SUM(total_amount) AS daily_revenue
  FROM transactions
  GROUP BY substr(transaction_date, 1, 10)
)
SELECT
  order_date,
  daily_revenue,
  CASE
    WHEN ROW_NUMBER() OVER (ORDER BY order_date) >= 7
    THEN AVG(daily_revenue) OVER (
      ORDER BY order_date
      ROWS BETWEEN 6 PRECEDING AND CURRENT ROW
    )
  END AS rolling_7d_avg
FROM daily_revenue_summary
ORDER BY order_date;

SELECT
  e1.employee_id AS employee_a,
  e2.employee_id AS employee_b,
  e1.manager_id
FROM employees e1
JOIN employees e2
  ON e1.manager_id = e2.manager_id
  AND e1.employee_id < e2.employee_id;

WITH RECURSIVE org AS (
  SELECT employee_id, manager_id, emp_name, 0 AS depth
  FROM employees
  WHERE manager_id IS NULL

  UNION ALL

  SELECT e.employee_id, e.manager_id, e.emp_name, o.depth + 1
  FROM employees e
  JOIN org o ON e.manager_id = o.employee_id
  WHERE o.depth < 20
)
SELECT employee_id, emp_name, depth FROM org WHERE depth > 0;