如何在navicat for mysql中修改课程表的结构，修改学分的数据类型，规定学分的取值

锁定表：LOCK TABLES tbl_name {READ | WRITE},[ tbl_name {READ | WRITE},…]

解锁表：UNLOCK TABLES！

select * from student where score between 50 and 60

改成绩

update student set score=score+5 where score between 50 and 60

所有的课程都不重复，你用distinct吗，用min吗？

select * from 表名 where 学分<(select 学分 from 表名 where 课程名='计算机网络')