Write SQL to compute current product stock

You need to generate a report showing the **current on-hand stock** for each product. Stock changes over time due to: - **Incoming shipments** (increase stock) - **Customer orders** (decrease stock) - **Customer returns** (increase stock) Assume the following tables: - `products(product_id, name)` - `inventory_baseline(product_id, baseline_qty)` — starting on-hand quantity (may be missing for some products) - `incoming_shipments(shipment_id, product_id, qty, received_at)` - `order_items(order_id, product_id, qty, ordered_at)` - `returns(return_id, product_id, qty, returned_at)` **Task:** Write a SQL query that returns one row per product: - `product_id` - `name` - `current_stock` Where: \[ \text{current_stock} = \text{baseline_qty} + \sum(\text{incoming qty}) + \sum(\text{return qty}) - \sum(\text{ordered qty}) \] Requirements: - Include products even if they have no shipments/orders/returns (treat missing quantities as 0). - Avoid double-counting due to join multiplication. - (Optional) If helpful, also show how you would filter to “as of” a given timestamp.