Interview Guides
You are given shipment event data from a defense supply chain workflow and need to produce accurate lead-time reporting for Lattice shipments. Some rows are duplicate event records for the same shipment and status, and some timestamps are missing. Write a PostgreSQL query that returns one row per shipment with a cleaned lead time in days from created_at to delivered time, using the earliest valid CREATED event and the latest valid DELIVERED event after deduplication. Exclude shipments where either side of the lead-time calculation is still null after cleaning.
