6.1ѯѧϰɼбΪk008γ̵ѧԳɼɼУ
	Select  Sid,Kcid,gradenum
	From   grade
	Where  kcid=k008
	Order by  gradenum  desc
6.2ѯNorthwind ݿproductsвƷĲƷʶƷ͵ۡΪͬԵλݽ
	Use northwind
	Select productid,productname,categoryid,unitprice
	From products
	Order by categoryid asc,unitprice desc
6.3ѯѧϰɼбΪk008γǰ3ѧĳɼ
	Select  top 3 Sid,Kcid,gradenum
	From   grade
	Where  kcid=k008
	Order by  gradenum  desc
6.4ѯѧϰɼпγе߷֡
	Select  max (gradenum)
	From  grade
6.5ѯѧϰɼСk009ſγ̵߷֡
	Select  max (gradenum)
	From   grade
	Where  kcid=k009
6.6ѯѧϢѧĸ
	Select count(*)  from student
6.7ѯѧϰɼиſγ̵߷֡
	Select  kcid, max (gradenum)
	From   grade
	Group by  kcid
6.8ѯѧϰɼиſγ̼ѧƽ֡
	Select  kcid,  avg(gradenum) as ѧƽɼ
	From   grade
	Where  gradenum >=60
	Group by  kcid
6.9ѧϰɼвѯпγƽɼ80ϵѧϢ
	Select  sid,  avg(gradenum) as ƽɼ
	From   grade
	Group by  sid  
	Having  avg(gradenum)>80
6.10ѧϰɼвѯk008ſγ̵ѧԳɼƽɼ
	Select  kcid,  gradenum
	From   grade
	Where kcid=k008
	Compute avg(gradenum)
6.11ѧϰɼвѯÿſγ̵ѧԳɼƽɼ
	Select  kcid,  gradenum
	From   grade
	Order by  kcid
	Compute avg(gradenum)  by kcid
6.12ѯμӡ缼γ̣k008Եѧѧš༶ͳɼ
	Select  s.sID , sName, sBanji, gradenum
	From   student  as  s  inner  join  grade   as  g  on  s.sid=g.sid
	Where  g.kcid ='k008'
6.13ѯμӡ缼γ̣k008Եѧѧš༶γͳɼ
	Select  s.sID , sName, sBanji, kcname , gradenum
	From   student  as  s  inner  join  grade   as  g  on  s.sid=g.sid 
	inner join course as c on c.kcid=g.kcid
	Where  g.kcid ='k008'
6.14ѯѧѧš༶μӿԵĿγ̱żɼ
	Select  s.sID , sName, sBanji, kcid,gradenum
	From   student  as  s  left  outer  join  grade   as  g  on  s.sid=g.sid
6.15ʹӵʽѯһʾÿѧſγ̳ɼ
	Select 	a.sid,a.kcid,a.gradenum,b.kcid,b.gradenum
	From   grade as a inner join grade as b on a.sid=b.sid
	where  a.kcid < b.kcid
6.16ʹӲѯѯÿѧƽ֡
	select distinct sid , ƽ=(select avg(gradenum) from grade b where b.sid =a.sid)
	from grade a
6.17ʹƽֵ70ѧѧš
	select distinct sid  
	from grade a
	where  (select avg(gradenum) from grade b where b.sid =a.sid)<70
6.18ѯһѧɼĿγ̵ڿνʦӲѯڲвѧĿγ̺
	select distinct kcjiaoshi  
	from course 
	where kcid= any (select kcid from grade where gradenum <60)
6.19ѯѧĿγ̵ڿνʦʹùؼinӲѯвѧѧšȻnot in ؼֶӲѯȡ£
	select distinct kcjiaoshi  
	from course 
	where kcid not in (select kcid from grade where gradenum <60)
6.20ѯƽֵȫѧƽֵѧѧţʹþۼavgӲѯһƽ֣ڶȫѧƽ֡£
	select distinct sid  
	from grade a
	where (select avg(gradenum) from grade b where a.sid=b.sid)
	      < (select avg(gradenum) from grade)
6.21ѯǷһŲѧʾѧź
	select distinct sid  ,sname
	from student s
	where exists (select * from grade g where g.gradenum<60 and g.sid=s.sid )
