SELECT COUNT(DISTINCT SNO)
FROM Student;

SELECT MAX(Score)
FROM Choose
WHERE CourseID = 'C1';

SELECT MIN(Score)
FROM Choose
WHERE CourseID = 'C1';

SELECT SUM(Score)
FROM Choose
WHERE CourseID = 'C1';

SELECT AVG(Score)
FROM Choose
WHERE CourseID = 'C1';

SELECT CourseID,CourseName
FROM Course
WHERE CourseBeforeID IS NULL;

SELECT Student.`SNO`,Student.`Name`,Course.`CourseName`,choose.`Score`
FROM student,choose,course
WHERE choose.`SNO` = student.`SNO` AND course.`CourseID` = choose.`CourseID`;

SELECT SNO,NAME,Age
FROM Student
WHERE College IN
(SELECT College
FROM Student
WHERE NAME = '张三'
);

SELECT *
FROM student stu1
WHERE EXISTS
(SELECT College
FROM student
WHERE stu1.`College` = college AND NAME = '张三'
);

SELECT sno,score
FROM choose
WHERE courseid='C1' and
score<any(SELECT score
from choose,student
where student.sno=choose.sno and name='张三' and courseid='C1');

SELECT SNO
FROM choose
WHERE CourseID = 'C1'
UNION
SELECT SNO
FROM choose
WHERE CourseID = 'C3';