select Sno as 学号,Sname as 姓名 from student;
select Sno,Sname from student;

select * from student;

select Sname as 姓名,(2014-Sage) as 出生年 from student;
select Sname ,(2014-Sage) from student;

select distinct Sno as 选修了课程的学生学号 from SC;
select distinct Sno from SC;

select Sname as 学生姓名 from student where Sdept='IS';

select Sname as 姓名,Sage as 年龄 from student where Sage<20;

select Sname as 姓名,Sdept as 系别,Sage as 年龄 from student where Sage between20 and 23;

select Sname as 姓名,Ssex as 性别 from student where Sdept='IS' or Sdept='CS';
select Sname as 姓名,Ssex as 性别 from student where Sdept in ('IS','CS');

select Sname as 姓名,Sage as 年龄 from student where Sdept !='IS'and Sdept!='CS';
select Sname as 姓名,Sage as 年龄 from student where Sdept not in('IS','MA');

select Sname as 姓名,Ssex as 性别 from student where Sname like '李%';

select Sno as 学号,Sname as 姓名,Sdept as 系别 from student where Sno like'2002%';

select * from student where Sname not like'刘%';

select Cno as 课程号,Cname as 课程名,Ccredit as 学分 from course where Cname like '%数据%';

select * from course where cname like '%数据%';包含数据的字符串 
select * from course where cname like '数据%';以数据开头的字符串
select * from course where cname like '%数据'; 以数据结尾的字符串

select Cno as 课程号,Cname as 课程名,Cpno from course where Cpno is null;

select Sno as 学号,Cno as 课程号,Grade as 成绩 from SC where Grade is not null;

select Sno as 学号,Grade as 成绩 from SC where Cno=3 order by Grade desc;

select Sno as 学号,Grade as 成绩 from SC where Cno=3 order by Grade asc;

select count(*) as 学生总数 from student;

select sum(Ccredit) as 所有课程总学分 from course;

select avg(Sage) as 平均年龄 from student;

select max(Grade) as 1号课程的最高分 from SC where Cno=1;

select Ssex as 性别,count(*) as 人数 from student group by Ssex;

select Cno as 课程号,avg(Grade) as 平均分 from SC group by Cno;

select Sno as 学号 ,count(course.Cno) as 选修课程数
From SC,course
Where course.Cno=SC.Cno
Group by Sno
Having Count(course.Cno)>=3;

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING aggregate_function(column_name) operator value

select Sno as 学号 ,count(course.Cno) as 选修课程数
From SC,course
Where course.Cno=SC.Cno and course.Cno !=1
Group by Sno
Having Count(course.Cno)>=2;

Select Sno
from sc
Where sc.Grade<60
Group by Sno
Having count(Cno)>=2;

Select Cno,count(Sno)
From SC
Group by Cno
Having count(sno)>=2

select student.Sno as 学号,course.Cno as 选修课号,SC.Grade as 成绩 
from student,course,SC 
where student.Sno=SC.Sno and course.Cno=SC.Cno ;

select SC.Sno as 学号,
FIRST.Cname as 直接选修课,
SECOND.Cname as 间接选修课
from SC,
course as FIRST,
course as SECOND
where FIRST.Cno=SC.Cno
and FIRST.Cpno=SECOND.Cno;

select student.Sno as 学号,
Sname as 姓名,
sc.Cno as 选修课程号
from student 
LEFT OUTER JOIN SC ON student.Sno=SC.Sno;

JOIN: 如果表中有至少一个匹配，则返回行
LEFT JOIN: 即使右表中没有匹配，也从左表返回所有的行
RIGHT JOIN: 即使左表中没有匹配，也从右表返回所有的行
FULL JOIN: 只要其中一个表中存在匹配，就返回行

UNION 操作符用于合并两个或多个 SELECT 语句的结果集。
请注意，UNION 内部的 SELECT 语句必须拥有相同数量的列。列也必须拥有相似的数据类型。同时，每条 SELECT 语句中的列的顺序必须相同。

select *
from student
where Sdept in (
 select Sdept
 from student
 where Sname='王敏'
);

select *
from student
where Sdept not in (
 select Sdept
 from student
 whereSname='王敏'
);

select student.Sno as 学号, Sname as 姓名
from student,SC
where student.Sno=SC.Sno and Cno in (
 select Cno
 from course
 where Cname='信息系统'
)

select distinct student.Sno as 学号, Sname as 姓名
from student,SC
where student.Sno=SC.Sno and Cno in (
 select Cno
 from SC,student
 where SC.Sno=student.Sno and student.Sno in (
 select Sno
 from student
 where student.Sname='刘晨'
 )
)

select *
from student
where Sdept=(
 select Sdept
 from student
 where Sname='王敏'
)

select Cno
from SC a
where Grade> (
 select min(Grade)
 from SC b
 where a.Cno=b.Cno
)

select Cno
from SC a
where Grade> (
 select avg(Grade)
 from SC b
 where a.Sno=b.Sno
)

select Sname as 姓名,Ssex as 性别, Sage as 年龄, Sdept as 所在系
from student
where Sage <(
 select Sage
 from student
 where Sdept='CS'
);

select Sname as 姓名, Sage as 年龄
from student
where Sdept<>'CS' and Sage <ALL (
 select Sage
 from student
 where Sdept='CS'
);

select Sname as 姓名
from student
where Exists (
 select *
 from SC
 where Cno=1 and Sno=Student.Sno
);

select *
from student
where student.Sdept='CS'
union
select *
from student
where student.Sage<=19;

Select *
from student,SC
where student.Sno=SC.Sno and SC.Cno=1
INTERSECT
Select *
from student
where student.Sage<=19;

select *
from student
where student.Sdept='SC'
EXCEPT
select *
from student
where student.Sage<=19;