查询“001”课程⽐“002”课程成绩⾼的所有学⽣的学号；select a.s_id from (select s_id,score from SC where C_ID='001') a,(select s_id,scorefrom SC where C_ID='002') b where a.score>b.score and a.s_id=b.s_id;
select中distinct10.查询平均成绩⼤于60分的同学的学号和平均成绩；
select S_ID,avg(score) from sc group by S_ID having avg(score) >60;
11.查询所有同学的学号、姓名、选课数、总成绩；
select Student.S_ID,Student.Sname,count(SC.C_ID),sum(score) from Student left Outer join SC on Student.S_ID=SC.S_ID group by Student.S_ID,Sname
12.查询姓“李”的⽼师的个数；
select count(distinct(Tname)) from Teacher where Tname like '李%';
13.查询所有课程成绩⼩于60分的同学的学号、姓名；
select S_ID,Sname from Student where S_ID not in (select S.S_ID from Student AS S,SC where S.S_ID
=SC.S_ID and score>60); 14.查询⾄少有⼀门课与学号为“1001”的同学所学相同的同学的学号和姓名；
select distinct S_ID,Sname from Student,SC where Student.S_ID=SC.S_ID and SC.C_ID in (select C_ID from SC where S_ID='1001');

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