python学习之老男孩python全栈第九期_数据库day004 -- 作业

https://www.cnblogs.com/YD2018/p/9451809.html

11. 查询学过“001”并且也学过编号“002”课程的同学的学号、姓名

select student.sid,student.sname from score LEFT JOIN student on score.student_id=student.sid where (course_id=1 or course_id=2) GROUP BY score.student_id having count(course_id)>1

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12. 查询学过“李平”老师所教的所有课的同学的学号、姓名

SELECT student.sid,student.sname from score LEFT JOIN student on score.student_id=student.sid where score.course_id in (SELECT course.cid from course where course.teacher_id=(select teacher.tid from teacher where teacher.tname='李平老师')) GROUP BY score.student_id having count(score.course_id) = (SELECT count(course.cid) from course where course.teacher_id=(select teacher.tid from teacher where teacher.tname='李平老师'));

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13. 查询有课程成绩小于60分的同学的学号、姓名

一. group by 做：

SELECT student.sid,student.sname from score LEFT JOIN student ON score.student_id=student.sid where score.num<60 group by score.student_id;

二. distinct  做：

去重：distinct -- 效率不高
SELECT distinct student.sid,student.sname from score LEFT JOIN student ON score.student_id=student.sid where score.num<60;

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14. 查询没有学全所有课的同学的学号、姓名

SELECT student.sid,student.sname from score LEFT JOIN student ON score.student_id=student.sid where score.course_id in (SELECT course.cid from course) GROUP BY score.student_id having count(score.course_id) !=(SELECT count(course.cid) from course);