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+# 作业
+
+
+
+```sql
+-- 1. 查询" 1 "课程比" 2 "课程成绩高的学生的信息（学号、姓名、性别、出生日期）及课程分数
+
+select * from student,score,if(score>) where student.student_id=score.student_id ;
+select * from student,score where student.student_id=score.student_id and course_id=1;
+select * from student,score where student.student_id=score.student_id and course_id=2;
+
+select * from (select * from student,score where student.student_id=score.student_id and course_id=1) li,(select * from student,score where student.student_id=score.student_id and course_id=2) jun where li.student_id=jun.student_id;
+
+
+-- 2. 查询同时参与" 1 "课程和" 2 "课程考试的学生信息
+
+select * from student where student_id in (select student_id from score where course_id=1) and student_id in (select student_id from score where course_id=2);
+
+
+-- 3. 查询存在" 1 "课程但可能不存在" 2 "课程的情况(不存在时显示为 null )
+
+select * from (select student_id from score where course_id=1) li left join (select student_id from score where course_id=2) jun on li.student_id=jun.student_id;
+-- 4. 查询不存在" 1 "课程但存在" 2 "课程的情况
+
+select * from (select student_id from score where course_id=1) li right join (select student_id from score where course_id=2) jun on li.student_id=jun.student_id;
+
+-- 5. 查询平均成绩大于等于 60 分的同学的学生编号、姓名和平均成绩
+select * from (
+select DISTINCT student.student_id,student.student_name,avg(score) over(partition by student.student_id) yang from student,score where student.student_id=score.student_id) lijunyang where yang>=60;
+
+-- 6. 查询在成绩表存在成绩的学生信息
+
+select * from student left join score on score.student_id=student.student_id where score is not null;
+
+-- 7. 查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为 null )
+
+select DISTINCT student.student_id,student_name,count(course_id) over(partition by student_id) li ,sum(score) over(partition by student_id)jun from student left join score on student.student_id=score.student_id;
+
+-- 8. 查询「李」姓老师的数量
+
+with aa as (select * from student),
+bb as (select * from score),
+cc as (select * from course),
+dd as (select * from teacher)
+select count(teacher_name) from aa left join bb on aa.student_id=bb.student_id left join cc on cc.course_id=bb.course_id left join dd on cc.teacher_id=dd.teacher_id where student_name like '李%';
+
+
+-- 9. 查询学过「李白」老师授课的同学的信息
+
+with aa as (select * from student),
+bb as (select * from score),
+cc as (select * from course),
+dd as (select * from teacher)
+select aa.* from aa left join bb on aa.student_id=bb.student_id left join cc on cc.course_id=bb.course_id left join dd on cc.teacher_id=dd.teacher_id where teacher_name = '李白';
+
+
+-- 10. 查询没有学全所有课程的同学的信息
+with aa as (select * from student),
+bb as (select * from score),
+cc as (select * from course),
+dd as (select * from teacher)
+select aa.* from aa left join bb on aa.student_id=bb.student_id left join cc on cc.course_id=bb.course_id left join dd on cc.teacher_id=dd.teacher_id where score is null;
+
+
+-- 11. 查询至少有一门课与学号为" 1 "的同学所学相同的同学的信息
+
+select DISTINCT student.* from student,score where student.student_id=score.student_id and course_id in (select course_id from student,score where student.student_id=score.student_id and student.student_id=1);
+
+-- 12. 查询和" 1 "号的同学学习的课程完全相同的其他同学的信息
+
+select * from (
+with aa as (select * from student),
+bb as (select * from score)
+select DISTINCT aa.student_id,student_name,sum(bb.course_id) over(partition by aa.student_id) li,count(bb.course_id) over(partition by aa.student_id) jun from aa,bb where aa.student_id=bb.student_id) lijunyang where li=(select DISTINCT sum(course_id) over(partition by score.student_id) from student,score where score.student_id=student.student_id and score.student_id=1) and jun=(select DISTINCT count(course_id) over(partition by score.student_id) from student,score where score.student_id=student.student_id and score.student_id=1) and student_id !=1;
+
+-- 13. 查询没学过「李白」老师讲授的任一门课程的学生姓名
+select student_name from student,score where student.student_id=score.student_id and score.course_id in (select course_id from course,teacher where course.teacher_id=teacher.teacher_id and teacher_name='李白');
+
+-- 14. 查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩
+
+select DISTINCT student.student_id,student_name,avg(score) over(partition by student_name) from score,student where score.student_id=student.student_id and score<60 and score.student_id in (select student_id from(
+select DISTINCT student_id,count(course_id) over(partition by student_id) from score)li);
+
+-- 15. 检索" 1 "课程分数小于 60，按分数降序排列的学生信息
+
+select * from score where course_id=1 and score<60 order by score desc;
+
+-- 16. 按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩
+select * from(
+select DISTINCT student_name,avg(score) over(partition by score.student_id ) avgg from score,student where student.student_id=score.student_id) li order by avgg desc;
+
+-- 17. 查询各科成绩最高分、最低分和平均分
+
+select DISTINCT course_name,max(score) over(partition by course.course_name) 最高分,min(score) over(partition by course.course_name) 最低分,avg(score) over(partition by course.course_name) 平均分 from score,course where course.course_id=score.course_id;
+
+
+-- 18. 以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率（及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90），要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列
+
+SELECT
+	score.course_id,
+	course.course_name,
+	max( score.score ) 最高分,
+	min( score.score ) 最低分,
+	avg( score.score ) 平均分,
+	(SUM(IF(score.score >= 60, 1, 0)) / COUNT(*) * 100) 及格率,
+	(SUM(IF(score.score >= 70 and score.score<80, 1, 0)) / COUNT(*) * 100) 中等率,
+	(SUM(IF(score.score >= 80 and score.score<90, 1, 0)) / COUNT(*) * 100) 优良率,
+	(SUM(IF(score.score >= 90, 1, 0)) / COUNT(*) * 100) 优秀率,
+	count(score.student_id) 选课人数
+FROM
+	score,
+	course 
+WHERE
+	course.course_id = score.course_id 
+GROUP BY
+	score.course_id;
+
+
+
+-- 19. 按各科成绩进行排序，并显示排名，Score 重复时保留名次空缺
+
+SELECT
+	student_name,
+	course_name,
+	score,
+	rank() OVER (partition by course.course_id ORDER BY score.score DESC)
+FROM
+	student,
+	score,
+	course 
+WHERE
+	student.student_id = score.student_id 
+	AND score.course_id = course.course_id 
+ORDER BY
+	course.course_id,score DESC;
+	
+
+-- 20. 按各科成绩进行排序，并显示排名，Score 重复时合并名次
+-- 21. 查询学生的总成绩，并进行排名，总分重复时保留名次空缺
+-- 22. 查询学生的总成绩，并进行排名，总分重复时不保留名次空缺
+-- 23. 统计各科成绩各分数段人数：课程编号，课程名称，[100-85]，[85-70]，[70-60]，[60-0] 及所占百分比
+-- 24. 查询各科成绩前三名的记录
+-- 25. 查询每门课程被选修的学生数
+-- 26. 查询出只选修两门课程的学生学号和姓名
+-- 27. 查询男生、女生人数
+-- 28. 查询名字中含有「风」字的学生信息
+-- 29. 查询同名同性学生名单，并统计同名人数
+-- 30. 查询 1990 年出生的学生名单
+-- 31. 查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列
+-- 32. 查询平均成绩大于等于 85 的所有学生的学号、姓名和平均成绩
+-- 33. 查询课程名称为「数学」，且分数低于 60 的学生姓名和分数
+-- 34. 查询所有学生的课程及分数情况（存在学生没成绩，没选课的情况）
+-- 35. 查询任何一门课程成绩在 70 分以上的姓名、课程名称和分数
+-- 36. 查询不及格的课程
+-- 37. 查询课程编号为 1 且课程成绩在 80 分以上的学生的学号和姓名
+-- 38. 求每门课程的学生人数
+-- 39. 成绩不重复，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩
+-- 40. 成绩有重复的情况下，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩
+-- 41. 查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩
+-- 42. 查询每门功成绩最好的前两名
+-- 43. 统计每门课程的学生选修人数（超过 5 人的课程才统计）。
+-- 44. 检索至少选修两门课程的学生学号
+-- 45. 查询选修了全部课程的学生信息
+-- 46. 查询各学生的年龄，只按年份来算
+-- 47. 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一
+-- 48. 查询本周过生日的学生
+-- 49. 查询下周过生日的学生
+-- 50. 查询本月过生日的学生
+-- 51. 查询下月过生日的学生
+```
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