Privacy-Preserving Analytics and Experimentation Questions

WITH grp AS (
  SELECT country, COUNT(*) AS n, SUM(amount) AS total
  FROM sales
  GROUP BY country
)
SELECT country,
       CASE WHEN n >= 5 THEN total ELSE NULL END AS total_masked,
       CASE WHEN n >= 5 THEN n ELSE NULL END AS n_masked
FROM grp;

WITH b AS (
  SELECT
    CASE
      WHEN age BETWEEN 18 AND 24 THEN '18-24'
      WHEN age BETWEEN 25 AND 34 THEN '25-34'
      ELSE '35+' END AS age_bucket,
    COUNT(*) AS n, SUM(amount) AS total
  FROM users JOIN sales USING(user_id)
  GROUP BY 1
)
SELECT age_bucket, total, n
FROM b
WHERE n >= 5;

-- Laplace noise example (conceptual; DB must support random functions)
WITH agg AS (
  SELECT country, COUNT(*) AS n, SUM(amount) AS total FROM sales GROUP BY country
)
SELECT country,
       n + CAST( ( -LN(RANDOM()) * sign - ) AS INT) AS n_noisy, -- pseudocode
       total + (RANDOM() - 0.5) * sensitivity * scale AS total_noisy
FROM agg;