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SELECT*FROM sc WHERE grade=NULL SELECT*FROM sc WHERE grade IS’’ SELECT*FROM sc WHERE grade IS NULL SELECT*FROM sc WHERE grade=’’
SELECT sno, cno FROM SC WHERE grade=NULL SELECT sno, cno FROM SC WHERE grade IS" SELECT sno, cno FROM SC WHERE grade IS NULL SELECT sno, cno FROM SC WHERE grade="
CNAME="数据库技术"AND S.SNO=SC.SNO AND SC.CNO=C.CNO CNAME="数据库技术" AND S.SNO=SC.SNO AND SC.CNO=CNO CNAME="数据库技术" AND S.SNO=SC.SNO AND SC.CNO=C.CNO CNAME="数据库技术" AND S.SNO=SC.SNO
SELECT sno,cno FROM SC WHERE grade=NULI SELECT sno,cno FROM SC WHERE grade Is SELECT sno,cno FROM SC WHERE grade IS NULL SELECT sno,cno FROM SC WHERE grade="
SELECT * FROM sc WHERE grade=NULL SELECT * FROM sc WHERE grade IS ‘ ’ SELECT * FROM sc WHERE grade IS NULL SELECT * FROM sc WHERE grade =‘ ’
SELECT * FROM sc WHERE grade=NULL SELECT * FROM sc WHERE grade IS ‘ ’ SELECT * FROM sc WHERE grade IS NULL SELECT * FROM sc WHERE grade =‘ ’
SELECT * FROM sc WHERE grade=NULL SELECT * FROM sc WHERE grade IS ‘ ’ SELECT * FROM sc WHERE grade IS NULL SELECT * FROM sc WHERE grade =‘ ’
CNAME=′数据库技术′AND S.SNO=SC.SNO AND SC.CNO=C.CNO CNAME=′数据库技术′AND S.SNO=SC.SNO AND SC.CNO=CNO CNAME=数据库技术 AND S.SNO=SC.SNO AND SC.CNO=C.CNO CNAME=′数据库技术′AND S.SNO=SC.SNO