数据库原理及安全（四）_数据库安全公式-优快云博客

这些SQL语句主要用于从学生、课程和成绩表中提取特定信息，例如查找与李勇同龄但不同名的学生，找出选修数据库课程的学生，比较学生年龄与特定学生或部门平均年龄，筛选高分或低分段的成绩，以及统计学生的平均分数和成绩计数等。

SELECT * from student
where Sage=(
SELECT Sage FROM student
WHERE Sname='李勇'
) AND Sname!='李勇'


SELECT Sno,Sname FROM student
WHERE Sno IN(
	SELECT Sno FROM sc
		WHERE Cno=(
			SELECT Cno FROM course
				WHERE Cname='数据库'
		)
)

SELECT Sno,Sname,Sage,Sdept
FROM student
WHERE Sage>(
SELECT Sage FROM student WHERE Sname='李勇'
)

SELECT Sno,Sname,Sage,Sdept
FROM student
WHERE Sage>(
SELECT AVG(Sage) FROM student WHERE Sdept='CS'
)

SELECT Sno,Sname,Sage,Sdept
FROM student
WHERE Sage>(
SELECT MAX(Sage) FROM student WHERE Sdept='CS'
) AND Sdept!='CS'

SELECT Sno,Cno FROM sc x
WHERE Grade>(
SELECT avg(Grade) FROM sc y WHERE x.Sno=y.Sno
)

SELECT Sno,Cno FROM sc x
WHERE Grade>(
SELECT avg(Grade) FROM sc y WHERE x.Cno=y.Cno
)

SELECT Sno,Sname,Sdept,Sage
FROM student x
WHERE Sage>(
SELECT AVG(Sage) FROM student y WHERE x.Sdept=y.Sdept
) 

#25
SELECT Sno, COUNT(*) AS Cnt, AVG(Grade) AS AveScore
FROM SC
GROUP BY Sno
HAVING min(Grade)>=60
ORDER BY AveScore DESC, Cnt DESC

SELECT Sno,Sname,Sdept
FROM student
WHERE Sage<(
SELECT min(Sage) FROM student WHERE Sdept='CS' 
) AND Sdept!='CS'

SELECT Sno,Grade FROM sc 
WHERE Grade>(
SELECT AVG(Grade) FROM sc WHERE Cno='1'
) AND Cno='1'

SELECT Sno,Sname,Sdept
FROM student x
WHERE Sage>(
SELECT AVG(Sage) FROM student y WHERE x.Sdept=y.Sdept
) 

#20
SELECT Sname FROM student
WHERE(
SELECT Sno NOT IN(
SELECT Sno FROM sc
WHERE Cno=(SELECT Cno FROM course WHERE Cname='数学')
)
)