1）．select 学号 from xsqk where 系别="01" 2）．Select xsqk.姓名,cj.成绩 from xsqk,cj where xsqk.学号=cj.学号 and (cj.课程号 in; (select 课程号 from kc where 课程名='c语言')) 3）．select * from xsqk where (系别="01" or 系别="02") and 学号 in (select 学号 from cj,kc; where cj.课程号=kc.课程号 and kc.课程名="c语言") 4）．select 课程名 from kc where 课程号 in (select distinct(课程号) from cj where 成绩>90) 5）．select xsqk.姓名,kc.课程名,cj.成绩 from xsqk,kc,cj where xsqk.学号=cj.学号 and; kc.课程号=cj.课程号 and cj.学号 in (select 学号 from xsqk where 入学成绩>500) 6）．select avg(入学成绩) from xsqk 7）．select 系别,count(*) from xsqk where 入学成绩>500 group by 系别 8）．select * from xsqka where 入学成绩<(select avg(入学成绩) from xsqkb where a.系别=b.系别) 恐怖啊，我现在越来越发现我与命令无缘！