给出一个产品库存表,列产品ID,仓库ID和数量,写一个UPDATE语句,从仓库1中所有产品的数量中减出1.
The UPDATE statement would be:

```
UPDATE product_inventory
SET Quantity = Quantity - 1
WHERE WarehouseID = 1;
``` 

This will update the Quantity column for all products in Warehouse 1 by subtracting 1 from their current Quantity value.