Geographic Mismatch — Impossible Travel

Same card, two cities, five minutes apart. Use LAG() over txn_at partitioned by account to grab each transaction's previous coordinates and time. Flag pairs where the geographic distance is more than 500 km AND the time gap is less than 30 minutes — physically impossible legitimate travel.

For distance, use a degree-distance approximation: SQRT((lat - prev_lat)^2 + (lng - prev_lng)^2) * 111 ≈ km (rough but fine for gross-mismatch detection). True Haversine accounts for longitude convergence at high latitudes; the approximation is close enough for fraud screening.

Show account_id, txn_id, prev_at, txn_at, km_from_prev (rounded to 0), minutes_from_prev (rounded to 1). Order by km_from_prev descending. Top 15.