diff --git "a/18\351\231\210\351\271\217/SQLQuery2.sql" "b/18\351\231\210\351\271\217/SQLQuery2.sql"
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index 0000000000000000000000000000000000000000..fb5922480c1a859fea2d35c3b149a25040f3a768
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+--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 sid, max(case when Cid ='01'then score else null end)语文,
+				max(case when cid ='02'then score else null end)数学,
+				max(case when cid ='03'then score else null end)英语,
+				AVG(score)平均成绩
+				 from sc 
+				 group by sid
+				 order by avg(score) desc;
+
+
+--14. 查询各科成绩最高分、最低分和平均分：
+
+	select 
+CId,
+(select Cname from Course c where c.CId = sc.CId)课程名称,
+MAX(score) 最高分,
+MIN(score) 最低分,
+AVG(score) 平均分,
+(
+	round(
+	(
+		(select COUNT(*) from SC sc2 where score >= 60 and sc2.CId = sc.CId group by CId)
+		 /
+		  1.0 
+		 / 
+		 (select COUNT(*) from SC sc2 where sc2.CId = sc.CId group by CId)
+		 ),2
+	 )
+) 及格率,
+(
+	round(
+	(
+		(select COUNT(*) from SC sc2 where score >= 70 and score <= 80 and sc2.CId = sc.CId group by CId)
+		 /
+		  1.0 
+		 / 
+		 (select COUNT(*) from SC sc2 where sc2.CId = sc.CId group by CId)
+		 ),2
+	 )
+) 中等率,
+(
+	round(
+	(
+		(select COUNT(*) from SC sc2 where score >= 80 and score <= 90 and sc2.CId = sc.CId group by CId)
+		 /
+		  1.0 
+		 / 
+		 (select COUNT(*) from SC sc2 where sc2.CId = sc.CId group by CId)
+		 ),2
+	 )
+) 优良率,
+(
+	round(
+	(
+		(select COUNT(*) from SC sc2 where score >= 90 and sc2.CId = sc.CId group by CId)
+		 /
+		  1.0 
+		 / 
+		 (select COUNT(*) from SC sc2 where sc2.CId = sc.CId group by CId)
+		 ),2
+	 )
+) 优秀率
+from SC sc
+group by CId
+
+
+
+
+
+--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
+
+
+
+--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 st.Sname,c.Cname,ROW_NUMBER()over(partition by s.cid order by score desc)排名  from SC s
+	join Student st on st.SId= s.SId
+	join Course c on c.CId= s.CId
+
+	
+
+
+--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 s.CId,st.Sname,c.Cname,rank()over(partition by s.cid order by score desc)排名  from SC s
+	join Student st on st.SId= s.SId
+	join Course c on c.CId= s.CId
+
+--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 a.SId,a.总分,dense_rank() over (order by 总分 desc) 排名 from
+			(select sid,sum(score) 总分 from sc group by sid ) a
+
+	
+--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 a.SId,a.总分,rank() over (order by 总分 desc) 排名 from
+			(select sid,sum(score) 总分 from sc group by sid ) a;
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