diff --git "a/13\345\217\267\351\203\221\346\226\207\346\272\220/\344\275\234\344\270\232/9.21\344\275\234\344\270\232.sql" "b/13\345\217\267\351\203\221\346\226\207\346\272\220/\344\275\234\344\270\232/9.21\344\275\234\344\270\232.sql"
new file mode 100644
index 0000000000000000000000000000000000000000..f23bc5b13918e7e4deb41419d971969b056c69af
--- /dev/null
+++ "b/13\345\217\267\351\203\221\346\226\207\346\272\220/\344\275\234\344\270\232/9.21\344\275\234\344\270\232.sql"
@@ -0,0 +1,41 @@
+
+select * from Student;
+select * from Course;
+select * from Teacher;
+
+--13. 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 a.sid,a.平均成绩,b.score from(select sid,score from sc) as b
+left join (select sid,SUM(score)/3 as 平均成绩 from SC 
+group by sid
+) as a on a.SId=b.SId
+order by a.平均成绩 desc
+
+
+--14. 查询各科成绩最高分、最低分和平均分：
+--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 a.CId,Cname,
+count(distinct b.SId) as 选修人数, 
+max(b.score), 
+min(b.score), 
+avg(b.score), 
+CONCAT(FLOOR(SUM(case when b.score>60 then 1 else 0 end)/1.0*100/count(distinct b.SId)),'%')  as '及格率', 
+CONCAT(FLOOR(SUM(case when b.score>=70 and b.score<80 then 1 else 0 end)/1.0*100/count(distinct b.SId)),'%') as '中等率', 
+CONCAT(FLOOR(SUM(case when b.score>=90 then 1 else 0 end)/1.0*100/count(distinct b.SId)),'%')as'优秀率',
+CONCAT(FLOOR(sum(case when b.score>=80 and b.score<90 then 1 else 0 end)/1.0*100/count(distinct b.SId)),'%') as '优良率'
+from Course as a left join sc as b on a.CId=b.CId 
+group by a.CId,a.Cname 
+order by 选修人数 DESC,a.CId 
+
+--15. 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 rank() over (partition by cid order by score desc) as 排名,cid,score from SC;
+
+--15.1 按各科成绩进行排序，并显示排名， Score 重复时合并名次
+select DENSE_RANK() over (partition by cid order by score desc) as 排名,cid,score from SC;
+--16. 查询学生的总成绩，并进行排名，总分重复时保留名次空缺
+select rank() over (order by sum(score) desc) as 排名,sid,sum(score) from SC group by sid 
+--16.1 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
+select DENSE_RANK() over (order by sum(score) desc) as 排名,sid,sum(score) from SC group by sid 
\ No newline at end of file
diff --git "a/13\345\217\267\351\203\221\346\226\207\346\272\220/\347\254\224\350\256\260/9.21\347\254\224\350\256\260.txt" "b/13\345\217\267\351\203\221\346\226\207\346\272\220/\347\254\224\350\256\260/9.21\347\254\224\350\256\260.txt"
new file mode 100644
index 0000000000000000000000000000000000000000..a0d3aa6943c72d44a88fb0009813df6b23a8d379
--- /dev/null
+++ "b/13\345\217\267\351\203\221\346\226\207\346\272\220/\347\254\224\350\256\260/9.21\347\254\224\350\256\260.txt"
@@ -0,0 +1,34 @@
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\ No newline at end of file