--含数据库
--1、查询"1"课程比"2"课程成绩高的所有学生的学号;
select d.S# from
(select b.S#,b.score as b_score,c.score as c_score from
(select S#,score from Sc WHERE C#=1) b inner join
(select S#,score from Sc WHERE C#=2) c on b.S#=c.S#) d
where d.b_score>d.c_score
--2、查询平均成绩大于60分的学号和平均成绩;
select S#,AVG(score) from Sc Group by S# having AVG(score)>60
--3、查询所有同学的学号、姓名、选课数、总成绩;
SELECT a.*,
CASE
WHEN Num IS null THEN 0
ELSE Num END AS '课程总数',
CASE
WHEN Total IS NULL THEN 0
ELSE Total END AS '总成绩'
FROM
(select S#,Sname from Student) a left join
(select S#,COUNT(*) AS Num,SUM(score) as Total from Sc Group BY S#) b --找所有同学的选课数和总成绩
on a.S#=b.S#
--4、查询姓"李"的老师个数;
select COUNT(*) from Teacher where Tname LIKE '李%'
--5、查询没学过"叶平"老师课的同学的学号、姓名;
--(把学过学生的学号先找出来)
SELECT d.* FROM Student d left join
(
select distinct a.S# from Sc a inner join
(select C# from Course where T#=
(select T# from Teacher where Tname='叶平')) b on a.C#=b.C#
) c on c.S#=d.S# where c.S# is null
--6、查询学过"1"并且也学过编号"2"课程的同学的学号、姓名;