场景1: 取max 表结构 create table tb_test_info( student_id char(4) comment '学号', grade_id int comment '课程号', score int comment '分数', primary key (student_id,grade_id) ); insert into tb_test_info(student_id,grade_id,score)values('001',1,97); insert into tb_test_info(student_id,grade_id,score)values('001