public interface StudentDao { //增 long add(Student student) throws SQLException; //删 boolean delete(long id) throws SQLException; //改 boolean update(Student student) throws SQLException; //查 //根据名字查询 List<Student> showOneN(String name) throws SQLException; //根据学号查询 Student showOneI(String id_num) throws SQLException; //查询全部 List<Student> showAll() throws SQLException; } <insert id="add" useGeneratedKeys="true" parameterType="com.task1.Student" keyProperty="id"> insert into student_info(create_at,update_at,name,qq,curricular,school_time,college,id_num,report_link,goal,refree)values(#{create_at},#{update_at},#{name},#{qq},#{curricular},#{school_time},#{college},#{id_num},#{report_link},#{goal},#{refree}) </insert> <delete id="delete" parameterType="long"> DELETE FROM student_info WHERE id=#{id} </delete> <update id="update" parameterType="com.task1.Student"> update student_info set id=#{id},create_at=#{create_at},update_at=#{update_at},name=#{name},qq=#{qq},curricular=#{curricular},school_time=#{school_time},college=#{college},report_link=#{report_link},goal=#{goal},refree=#{refree} where id_num=#{id_num} </update> <select id="showAll" resultType="com.task1.Student"> SELECT *from student_info </select> <select id="showOneN" resultType="com.task1.Student"> select * from student_info WHERE NAME =#{name} </select> <select id="showOneI" resultType="com.task1.Student"> SELECT *from student_info WHERE id_num=#{id_num} </select> mybatis的接口方法里的参数类型、返回值类型与mybatis的映射文件里sql语句的parameterType、resultType一定要匹配吗？它们指定的是一个东西的类型吗？为什么要重复去指定参数类型？