第一题：select SC1.S# from SC SC1 JOIN SC SC2 ON SC1.S#=SC2.S# WHERE SC1.C#='001' AND SC2.C#='002' AND SC1.score>SC2.score;
第二题：select S#,AVG(score) as '平均成绩' from SC group by S# having AVG(score)>60;
第三题：select count(1) from Teacher where Tname like '％li';
第四题：
