正常增删改的返回值只是int类型代表影响行数，或bool类型，表示成功或失败

<insert id="addUser" useGeneratedKeys="true" keyProperty="uid">
    insert into users values(null, #{uname}, #{uage})
</insert>

= new User(null, "test", 13);
 mapper.addUser(user);
 session.commit();

 System.out.println(user.getUid());