ASELECT*TOP 20 FROM SC ORDER BY成绩WHERE课程号=”2002”
BSELECT*PERCENT 20 FROM SC ORDER BY成绩DESCWHERE课程号=”2002”
CSELECT*TOP 20 PERCENT FROM SC ORDER BY成绩WHERE课程号=”2002”
DSELECT*TOP 20 PERCENT FROM SC ORDER BY成绩DESCWHERE课程号=”2002”