SQL MERGE (Standard Upsert)

-- PostgreSQL 15+ MERGE syntax
MERGE INTO products AS target
USING staging_products AS source
ON target.sku = source.sku
WHEN MATCHED AND source.price <> target.price THEN
  UPDATE SET
    price = source.price,
    updated_at = NOW()
WHEN NOT MATCHED THEN
  INSERT (sku, name, price, created_at)
  VALUES (source.sku, source.name, source.price, NOW())
WHEN NOT MATCHED BY SOURCE THEN
  UPDATE SET
    is_active = false;