1.从另一张表中选择数据插入新表中
INSERT INTO orders (ISBN) SELECT DISTINCT ISBN FROM new_ratings;
2.报错You can't specify target table 'new_ratings' for update in FROM clause
UPDATE new_ratings SET bookid = (SELECT (orders.id) FROM orders,new_ratings WHERE orders.ISBN = new_ratings.ISBN)
修改后为：
update new_ratings join orders on new_ratings.ISBN=orders.ISBN set new_ratings.bookid=orders.id
3.修改字段类型
alter table student alter column sno varchar(10)
