You need to merge (upsert) customer records from a CSV import — insert new, update existing. How in PostgreSQL?

PostgreSQL 15+ MERGE statement: MERGE INTO customers AS target USING staging_customers AS source ON target.email = source.email WHEN MATCHED THEN UPDATE SET name=source.name, phone=source.phone, updated_at=NOW() WHEN NOT MATCHED THEN INSERT (email, name, phone, created_at) VALUES (source.email, source.name, source.phone, NOW()); PostgreSQL INSERT ON CONFLICT (all versions): INSERT INTO customers (