SQL

ÌâÄ¿1:
ÎÊÌâÃèÊö:
 S (SNO,SNAME) ѧÉú¹Øϵ¡£SNO ΪѧºÅ£¬SNAME ΪÐÕÃû
 C (CNO,CNAME,CTEACHER) ¿Î³Ì¹Øϵ¡£CNO Ϊ¿Î³ÌºÅ£¬CNAME Ϊ¿Î³ÌÃû£¬CTEACHER ΪÈονÌʦ
 SC(SNO,CNO,SCGRADE) Ñ¡¿Î¹Øϵ¡£SCGRADE Ϊ³É¼¨
 1.£¨1£©ÕÒ³öÑ¡ÐÞ¹ý“ÀîÃ÷”ÀÏʦ½²Êڿγ̵ÄËùÓÐѧÉúÐÕÃû
 --ʵÏÖ´úÂë:·¨Ò»
Select *
from SC,C,S
Where SC.CNO=C.CNO AND SC.SNO=S.SNO AND CTEACHER='ÀîÃ÷'
---·¨¶þ£º-------------
Select *
from S
Where Sno IN( Select Sno
              from C,SC
              Where C.[Cno]=SC.[Cno] AND CTEACHER='ÀîÃ÷')
 
£¨2£©ÕÒ³öûÓÐÑ¡ÐÞ¹ý“ÀîÃ÷”ÀÏʦ½²Êڿγ̵ÄËùÓÐѧÉúÐÕÃû
 --ʵÏÖ´úÂë:·¨Ò»
Select SName
from S
Where [Sno] NOT IN( Select SC.[Sno]
                    from SC,C
                    Where SC.CNO=C.CNO AND CTEACHER='ÀîÃ÷')
 
£¨3£©ÕÒ³öûÓÐÑ¡ÐÞ¹ý¿Î³ÌºÅΪ"1"µÄËùÓÐѧÉúÐÕÃû
 --ʵÏÖ´úÂë
Select SName
from S
Where [Sno] NOT IN( Select [Sno] from SC Where CNO='1')
 
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 2. ÁгöÓжþÃÅÒÔÉÏ(º¬Á½ÃÅ)²»¼°¸ñ¿Î³ÌµÄѧÉúÐÕÃû¼°Æäƽ¾ù³É¼¨
 --ʵÏÖ´úÂë:
Select S.SNO,S.SNAME,AVG_SCGRADE=AVG(SC.SCGRADE)
from S,SC,( Select SNO
                     from SC
                     Where SCGRADE<60
                     GROUP BY SNO
  &nb