关系模式如下：Product(maker,model,type)PC(model,speed,ram,hd,price)Printer(model,color,type,price)Laptop(model,speed,ram,hd,price)用SQL表达查询厂商B生产的所有产品的型号和价格如下，SELECT model, priceFROM product pcWHERE maker=”B”UNIONSELECT model, priceFROM product printerWHERE maker=”B”UNIONSELECT model, priceFROM product laptopWHERE maker=”B”写成以上形式是否正确。（ ）