select Sno,Sname,Smajor from Student  
select Sname,Sbirthdate,Smajor from Student

SELECT Sno
FROM SC
GROUP BY Sno//按学号分组
HAVING COUNT(Cno) >=3

select SUM(Grade)Sum_credit from Student s left join SC on s.Sno='20180001'

select Sno,Sname from Student where Smajor like '%信息系统%'

select Sname from Student where Sname not like '%刘%'
DATEDIFF(year,Sbitthday.GETDATE())
select Sname from Student where DATEDIFF(year,Sbirthdate,GETDATE()) < 20 and Smajor like'计算机'
INSERT INTO Student (Sno, Sname, Ssex, Sbirthdate) 
VALUES ('20180009', '李刚', '男', '2001-5-6');


select Sname from Student where DATEDIFF(year,Sbirthdate,GETDATE()) < 20 

SELECT COUNT(*) AS TotalStudents
FROM Student
WHERE Sbirthdate >= '2000-01-01';

SELECT COUNT(*) AS TotalStudents
FROM Student
WHERE Sbirthdate >= '2000-01-01';

select * ,DATEDIFF(year,Sbirthdate,GETDATE()) as sage from Student where Sbirthdate >= '2000-01-01';

SELECT Sname
FROM Student
WHERE Sno IN (SELECT Sno FROM Sc WHERE Grade >= 80);


SELECT *
FROM Student
WHERE Sbirthdate >= '2000-01-01' AND Sbirthdate <= '2001-12-31';


SELECT Sname,Ssex
FROM Student
WHERE Smajor <> '信息管理与系统' AND Smajor <> '计算机科学与技术';


SELECT COUNT(*) AS Scount
FROM Student
WHERE DATEDIFF(year,Sbirthdate,GETDATE()) > 20


SELECT *
FROM Student
WHERE Sname LIKE '王__';

update SC set grade=NULL where sno=20180001 and cno=81001


    select * from Student s left join SC sc on s.Sno = sc.sno order by Smajor asc,Sbirthdate desc
    select Cno,COUNT(1)as hehe from Student s left join SC sc on s.Sno = sc.sno where Cno is not null group by Cno
    
    select AVG(Grade)avg_grade from student s left join SC on s.Sno = SC.Sno where Cno = '81001'
    
SELECT Cno
FROM Course
GROUP BY Cno;


update [Student] set Sbirthdate = DATEADD(YEAR,1,Sbirthdate) where Ssex = '女'


SELECT MAX(Grade) AS max_grade
FROM Sc
WHERE Cno = 81001;

select distinct Sno from sc

SELECT COUNT(DISTINCT Sno) AS Scount
FROM sc;