1. 使用UPDATE

UPDATE product p, product_price pp SET pp.price = p.price * 0.8 WHERE p.productid= pp.productId;

2. 通过INNER JOIN

UPDATE product p INNER JOIN product_price pp ON p.productid= pp.productid SET pp.price = p.price * 0.8;
3.通过LEFT JOIN

UPDATE product p LEFT JOIN product_price pp ON p.productid= pp.productid SET p.isdelete = 1 WHERE pp.productid IS NULL;
4. 通过子查询

UPDATE product_price pp SET price=(SELECT price*0.8 FROM product WHERE productid = pp.productid);