经典sql练习题50道

材料

材料说明

学生表，教师表，教师课程表，学生课程成绩表。
一个老是带一门课。一个学生可选，多选，不选课程。

库

-- 导出 nero_sql_practice 的数据库结构
CREATE DATABASE IF NOT EXISTS `nero_sql_practice` /*!40100 DEFAULT CHARACTER SET utf8 */;
USE `nero_sql_practice`;

表

-- 导出  表 nero_sql_practice.course 结构
CREATE TABLE IF NOT EXISTS `course` (
  `CId` varchar(10) DEFAULT NULL,
  `Cname` varchar(10) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL,
  `TId` varchar(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- 导出  表 nero_sql_practice.sc 结构
CREATE TABLE IF NOT EXISTS `sc` (
  `SId` varchar(10) DEFAULT NULL,
  `CId` varchar(10) DEFAULT NULL,
  `score` decimal(18,1) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- 导出  表 nero_sql_practice.student 结构
CREATE TABLE IF NOT EXISTS `student` (
  `SId` varchar(10) DEFAULT NULL,
  `Sname` varchar(10) DEFAULT NULL,
  `Sage` datetime DEFAULT NULL,
  `Ssex` varchar(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

-- 导出  表 nero_sql_practice.teacher 结构
CREATE TABLE IF NOT EXISTS `teacher` (
  `TId` varchar(10) DEFAULT NULL,
  `Tname` varchar(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

数据

-- 正在导出表  nero_sql_practice.course 的数据：~3 rows (大约)
/*!40000 ALTER TABLE `course` DISABLE KEYS */;
INSERT INTO `course` (`CId`, `Cname`, `TId`) VALUES
	('01', '语文', '02'),
	('02', '数学', '01'),
	('03', '英语', '03');
/*!40000 ALTER TABLE `course` ENABLE KEYS */;

-- 正在导出表  nero_sql_practice.sc 的数据：~18 rows (大约)
/*!40000 ALTER TABLE `sc` DISABLE KEYS */;
INSERT INTO `sc` (`SId`, `CId`, `score`) VALUES
	('01', '01', 80.0),
	('01', '02', 90.0),
	('01', '03', 99.0),
	('02', '01', 70.0),
	('02', '02', 60.0),
	('02', '03', 80.0),
	('03', '01', 80.0),
	('03', '02', 80.0),
	('03', '03', 80.0),
	('04', '01', 50.0),
	('04', '02', 30.0),
	('04', '03', 20.0),
	('05', '01', 76.0),
	('05', '02', 87.0),
	('06', '01', 31.0),
	('06', '03', 34.0),
	('07', '02', 89.0),
	('07', '03', 98.0);
/*!40000 ALTER TABLE `sc` ENABLE KEYS */;

-- 正在导出表  nero_sql_practice.student 的数据：~12 rows (大约)
/*!40000 ALTER TABLE `student` DISABLE KEYS */;
INSERT INTO `student` (`SId`, `Sname`, `Sage`, `Ssex`) VALUES
	('01', '赵雷', '1990-01-01 00:00:00', '男'),
	('02', '钱电', '1990-12-21 00:00:00', '男'),
	('03', '孙风', '1990-12-20 00:00:00', '男'),
	('04', '李云', '1990-12-06 00:00:00', '男'),
	('05', '周梅', '1991-12-01 00:00:00', '女'),
	('06', '吴兰', '1992-01-01 00:00:00', '女'),
	('07', '郑竹', '1989-01-01 00:00:00', '女'),
	('09', '张三', '2017-12-20 00:00:00', '女'),
	('10', '李四', '2017-12-25 00:00:00', '女'),
	('11', '李四', '2012-06-06 00:00:00', '女'),
	('12', '赵六', '2013-06-13 00:00:00', '女'),
	('13', '孙七', '2014-07-09 00:00:00', '女');
/*!40000 ALTER TABLE `student` ENABLE KEYS */;

-- 正在导出表  nero_sql_practice.teacher 的数据：~3 rows (大约)
/*!40000 ALTER TABLE `teacher` DISABLE KEYS */;
INSERT INTO `teacher` (`TId`, `Tname`) VALUES
	('01', '张三'),
	('02', '李四'),
	('03', '王五');

练习题

1. 查询" 01 “课程比” 02 "课程成绩高的学生的信息及课程分数

   SELECT t1.Sid, t1.Cid AS cid01, t1.Score AS score01, t2.Cid AS cid02, t2.Score AS score02
	FROM (SELECT * FROM sc WHERE sc.CId = '01') AS t1 INNER JOIN (SELECT * FROM sc WHERE sc.CId = '02') AS t2
	ON t1.Sid = t2.Sid;

1.1 查询同时存在" 01 “课程和” 02 "课程的情况

	SELECT student.*, temp1and2.score01, temp1and2.score02 FROM
		(SELECT t1.Sid, t1.Cid AS cid01, t1.Score AS score01, t2.Cid AS cid02, t2.Score AS score02
		FROM (SELECT * FROM sc WHERE sc.CId = '01') AS t1 INNER JOIN (SELECT * FROM sc WHERE sc.CId = '02') AS t2
		ON t1.Sid = t2.Sid) AS temp1and2
	LEFT JOIN student ON temp1and2.SId = student.SId;

1.2 查询存在" 01 “课程但可能不存在” 02 "课程的情况(不存在时显示为 null )

	SELECT student.*, temp1and2.score01, temp1and2.score02 FROM
		(SELECT t1.Sid, t1.Cid AS cid01, t1.Score AS score01, t2.Cid AS cid02, t2.Score AS score02
		FROM (SELECT * FROM sc WHERE sc.CId = '01') AS t1 LEFT JOIN (SELECT * FROM sc WHERE sc.CId = '02') AS t2
		ON t1.Sid = t2.Sid) AS temp1and2
	LEFT JOIN student ON temp1and2.SId = student.SId;

1.3 查询不存在" 01 “课程但存在” 02 "课程的情况

	SELECT student.*, temp1and2.score01, temp1and2.score02 FROM
		(SELECT t1.Sid, t1.Cid AS cid01, t1.Score AS score01, t2.Cid AS cid02, t2.Score AS score02
		FROM (SELECT * FROM sc WHERE sc.CId = '01') AS t1 RIGHT JOIN (SELECT * FROM sc WHERE sc.CId = '02') AS t2
		ON t1.Sid = t2.Sid) AS temp1and2
	LEFT JOIN student ON temp1and2.SId = student.SId;

2. 查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩

	SELECT SId, AVG(score) AS avgScore FROM sc GROUP BY Sid;
	SELECT student.*, t1.avgScore FROM (SELECT SId AS SId, AVG(score) AS avgScore FROM sc GROUP BY Sid) AS t1 INNER JOIN student ON t1.SId = student.SId;

3. 查询在 SC 表存在成绩的学生信息

	SELECT student.* FROM student INNER JOIN sc ON student.SId = sc.SId;
	SELECT student.* FROM student LEFT JOIN sc ON student.SId = sc.SId;
	SELECT student.* FROM student RIGHT JOIN sc ON student.SId = sc.SId;
	
	SELECT student.* FROM student INNER JOIN sc ON sc.SId = student.SId;
	SELECT student.* FROM student LEFT JOIN sc ON sc.SId = student.SId;
	SELECT student.* FROM student RIGHT JOIN sc ON sc.SId = student.SId;
	
	SELECT student.*, sc.* FROM student INNER JOIN sc ON student.SId = sc.SId;
	SELECT student.*, sc.*  FROM student LEFT JOIN sc ON student.SId = sc.SId;
	SELECT student.*, sc.*  FROM student RIGHT JOIN sc ON student.SId = sc.SId;
	
	SELECT student.*, sc.*  FROM student INNER JOIN sc ON sc.SId = student.SId;
	SELECT student.*, sc.*  FROM student LEFT JOIN sc ON sc.SId = student.SId;
	SELECT student.*, sc.*  FROM student RIGHT JOIN sc ON sc.SId = student.SId;
	
	SELECT student.* FROM student INNER JOIN (SELECT * FROM sc GROUP BY SId) AS t1 ON student.SId = t1.SId;
	SELECT student.* FROM student WHERE SId IN (SELECT SId FROM sc);

4. 查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为 null )

	SELECT sc.*, COUNT(1) AS classCount, SUM(score) AS totalScore FROM sc GROUP BY SId;
	SELECT student.*, t1.classCount, t1.totalScore FROM student LEFT JOIN (SELECT sc.SId AS SId, COUNT(1) AS classCount, SUM(score) AS totalScore FROM sc GROUP BY SId) AS t1 ON student.SId = t1.SId;

4.1 查有成绩的学生信息

	SELECT student.* FROM student WHERE SId IN (SELECT SId FROM sc);

5. 查询「李」姓老师的数量

	SELECT COUNT(1) FROM teacher WHERE teacher.Tname LIKE '李%';

6. 查询学过「张三」老师授课的同学的信息

	SELECT TId FROM teacher WHERE Tname = '张三';
	SELECT CId FROM course WHERE TId = '01';
	SELECT SId FROM sc WHERE CId = '02';
	
	SELECT * FROM student WHERE SId IN (
		SELECT SId FROM sc WHERE CId IN (
			SELECT CId FROM course WHERE TId IN (
				SELECT TId FROM teacher WHERE Tname = '张三'
			)
		)
	);

7. 查询没有学全所有课程的同学的信息

	SELECT COUNT(1) FROM course;
	SELECT sc.`*`, COUNT(1) AS count FROM sc GROUP BY SId;
	SELECT SId FROM (SELECT sc.`*`, COUNT(1) AS totalCount FROM sc GROUP BY SId) AS t1 WHERE t1.totalCount < (SELECT COUNT(1) FROM course);
	
	SELECT * FROM student WHERE SId IN (
		SELECT SId FROM (
			SELECT sc.* , COUNT(1) AS totalCount FROM sc GROUP BY SId
		) AS t1 WHERE t1.totalCount < (SELECT COUNT(1) FROM course)
	);

8. 查询至少有一门课与学号为" 01 "的同学所学相同的同学的信息

	SELECT CId FROM sc WHERE SId = '01';
	SELECT SId FROM sc WHERE CId IN (SELECT CId FROM sc WHERE SId = '01') AND SId != '01';
	SELECT * FROM student WHERE SId IN (SELECT SId FROM sc WHERE CId IN (SELECT CId FROM sc WHERE SId = '01') AND SId != '01');

9. 查询和" 01 "号的同学学习的课程完全相同的其他同学的信息

	SELECT SId, COUNT(1) AS totalCount FROM sc WHERE SId != '01' GROUP BY SId HAVING totalCount = 3;
	SELECT * FROM student WHERE SId IN (SELECT SId FROM ( SELECT SId, COUNT(1) AS totalCount FROM sc WHERE SId != '01' GROUP BY SId HAVING totalCount = 3) AS t1);
	SELECT * FROM student WHERE SId IN (SELECT SId FROM sc WHERE SId != '01' GROUP BY SId HAVING COUNT(1) = 3);

10. 查询没学过"张三"老师讲授的任一门课程的学生姓名

	SELECT TId FROM teacher WHERE Tname = '张三';
	SELECT CId FROM course WHERE TId IN (SELECT TId FROM teacher WHERE Tname = '张三');
	SELECT SId FROM sc WHERE Cid IN (SELECT CId FROM course WHERE TId IN (SELECT TId FROM teacher WHERE Tname = '张三'));
	SELECT * FROM student WHERE SId NOT IN (SELECT SId FROM sc WHERE Cid IN (SELECT CId FROM course WHERE TId IN (SELECT TId FROM teacher WHERE Tname = '张三')));

11. 查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩

	SELECT SId, AVG(score) AS avgScore FROM sc WHERE score < 60 GROUP BY SId HAVING COUNT(1) >= 2 ;
	SELECT SId, AVG(score) AS avgScore FROM sc WHERE SId IN (SELECT SId FROM sc WHERE score < 60 GROUP BY SId HAVING COUNT(1) >= 2) GROUP BY SId;
	SELECT student.*, t1.avgScore FROM student INNER JOIN (SELECT SId, AVG(score) AS avgScore FROM sc WHERE SId IN (SELECT SId FROM sc WHERE score < 60 GROUP BY SId HAVING COUNT(1) >= 2) GROUP BY SId) AS t1 ON student.SId = t1.SId;

12. 检索" 01 "课程分数小于 60，按分数降序排列的学生信息

	SELECT * FROM sc WHERE CId = '01' AND score < 60;
	SELECT student.*, t1.score FROM student INNER JOIN (SELECT * FROM sc WHERE CId = '01' AND score < 60) AS t1 ON student.SId = t1.SId ORDER BY t1.score DESC;

13. 按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩

	SELECT sc.SId,  SUM(score) AS totalScore, AVG(score) AS avgScore FROM sc GROUP BY SId ORDER BY avgScore DESC;
	SELECT student.`*`, t1.totalScore, t1.avgScore FROM student LEFT JOIN (SELECT sc.SId,  SUM(score) AS totalScore, AVG(score) AS avgScore FROM sc GROUP BY SId) AS t1 ON student.SId = t1.SId ORDER BY avgScore DESC;

14. 查询各科成绩最高分、最低分和平均分

以如下形式显示：课程 ID，课程 name，最高分，最低分，平均分，及格率，中等率，优良率，优秀率
及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90
要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列

   
	SELECT CId, MAX(score) AS maxScore, MIN(score) AS minScore, AVG(score) AS avgScore, COUNT(1) AS studentCount FROM sc GROUP BY CId ORDER BY studentCount DESC , CId ASC;
	SELECT CId, COUNT(1) AS studentCount, SUM(if(score >= 90, 1, 0)) AS a, SUM(if(score >= 90, 1, 0)) / COUNT(1) AS aPrecent FROM sc GROUP BY CId ORDER BY studentCount DESC , CId ASC;
	SELECT CId, MAX(score) AS maxScore, MIN(score) AS minScore, AVG(score) AS avgScore, COUNT(1) AS studentCount, 
		SUM(IF(score >= 90, 1, 0)) AS a, SUM(IF(score >= 90, 1, 0)) / COUNT(1) AS aPrecent,
		SUM(IF(score < 90, IF(score >= 80, 1, 0), 0)) AS b, SUM(IF(score < 90, IF(score >= 80, 1, 0), 0)) / COUNT(1) AS bPrecent,
		SUM(IF(score < 80, IF(score >= 70, 1, 0), 0)) AS c, SUM(IF(score < 80, IF(score >= 70, 1, 0), 0)) / COUNT(1) AS cPrecent,
		SUM(IF(score < 70, IF(score >= 60, 1, 0), 0)) AS d, SUM(IF(score < 70, IF(score >= 60, 1, 0), 0)) / COUNT(1) AS dPrecent,
		SUM(IF(score < 60, 1, 0)) AS e, SUM(IF(score < 60, 1, 0)) / COUNT(1) AS ePrecent
		FROM sc GROUP BY CId ORDER BY studentCount DESC , CId ASC;

	SELECT course.Cname, t1.* FROM course INNER JOIN (
		SELECT CId, MAX(score) AS maxScore, MIN(score) AS minScore, AVG(score) AS avgScore, COUNT(1) AS studentCount, 
			SUM(IF(score >= 90, 1, 0)) AS a, SUM(IF(score >= 90, 1, 0)) / COUNT(1) AS aPrecent,
			SUM(IF(score < 90, IF(score >= 80, 1, 0), 0)) AS b, SUM(IF(score < 90, IF(score >= 80, 1, 0), 0)) / COUNT(1) AS bPrecent,
			SUM(IF(score < 80, IF(score >= 70, 1, 0), 0)) AS c, SUM(IF(score < 80, IF(score >= 70, 1, 0), 0)) / COUNT(1) AS cPrecent,
			SUM(IF(score < 70, IF(score >= 60, 1, 0), 0)) AS d, SUM(IF(score < 70, IF(score >= 60, 1, 0), 0)) / COUNT(1) AS dPrecent,
			SUM(IF(score < 60, 1, 0)) AS e, SUM(IF(score < 60, 1, 0)) / COUNT(1) AS ePrecent
		FROM sc GROUP BY CId ORDER BY studentCount DESC , CId ASC
	) AS t1 ON course.CId = t1.CId;

15. 按各科成绩进行排序，并显示排名， Score 重复时保留名次空缺

	SELECT *, RANK() OVER(ORDER BY score DESC) AS ranking FROM sc;
	SELECT *, DENSE_RANK() OVER(ORDER BY score DESC) AS ranking FROM sc;
	SELECT *, RANK() OVER(PARTITION BY CId ORDER BY score DESC) AS ranking FROM sc ORDER BY CId DESC;

15.1 按各科成绩进行排序，并显示排名， Score 重复时合并名次

	SELECT *, DENSE_RANK() OVER(PARTITION BY CId ORDER BY score DESC) AS ranking FROM sc ORDER BY CId DESC;

16. 查询学生的总成绩，并进行排名，总分重复时保留名次空缺

	SELECT *, SUM(score) AS totalScore FROM sc GROUP BY SId;
	SELECT *, RANK() OVER(ORDER BY totalScore DESC) FROM (SELECT *, SUM(score) AS totalScore FROM sc GROUP BY SId) AS t1 ORDER BY t1.totalScore DESC;

16.1 查询学生的总成绩，并进行排名，总分重复时不保留名次空缺

	SELECT *, DENSE_RANK() OVER(ORDER BY totalScore DESC) FROM (SELECT *, SUM(score) AS totalScore FROM sc GROUP BY SId) AS t1 ORDER BY t1.totalScore DESC;

17. 统计各科成绩各分数段人数：

课程编号，课程名称，[100-85]，[85-70]，[70-60]，[60-0] 及所占百分比

	SELECT course.Cname, t1.* FROM course INNER JOIN (
		SELECT CId, MAX(score) AS maxScore, MIN(score) AS minScore, AVG(score) AS avgScore, COUNT(1) AS studentCount, 
			SUM(IF(score >= 90, 1, 0)) AS a, SUM(IF(score >= 90, 1, 0)) / COUNT(1) AS aPrecent,
			SUM(IF(score < 90, IF(score >= 80, 1, 0), 0)) AS b, SUM(IF(score < 90, IF(score >= 80, 1, 0), 0)) / COUNT(1) AS bPrecent,
			SUM(IF(score < 80, IF(score >= 70, 1, 0), 0)) AS c, SUM(IF(score < 80, IF(score >= 70, 1, 0), 0)) / COUNT(1) AS cPrecent,
			SUM(IF(score < 70, IF(score >= 60, 1, 0), 0)) AS d, SUM(IF(score < 70, IF(score >= 60, 1, 0), 0)) / COUNT(1) AS dPrecent,
			SUM(IF(score < 60, 1, 0)) AS e, SUM(IF(score < 60, 1, 0)) / COUNT(1) AS ePrecent
		FROM sc GROUP BY CId ORDER BY studentCount DESC , CId ASC
	) AS t1 ON course.CId = t1.CId;

18. 查询各科成绩前三名的记录

	SELECT *, DENSE_RANK() OVER(PARTITION BY CId ORDER BY score DESC) AS ranking FROM sc ORDER BY CId DESC;
	SELECT * FROM (SELECT *, DENSE_RANK() OVER(PARTITION BY CId ORDER BY score DESC) AS ranking FROM sc ORDER BY CId DESC) AS t1 WHERE t1.ranking <= 3;

19. 查询每门课程被选修的学生数

	SELECT CId, COUNT(1) AS totalCount FROM sc GROUP BY CId;

20. 查询出只选修两门课程的学生学号和姓名

	SELECT Sid FROM sc GROUP BY SId HAVING COUNT(1) = 2;
	SELECT * FROM student WHERE SId IN(SELECT Sid FROM sc GROUP BY SId HAVING COUNT(1) = 2);

21. 查询男生、女生人数

	SELECT SUM(IF(Ssex = '男', 1, 0)) AS male, SUM(IF(Ssex = '女', 1, 0)) AS female FROM student;

22. 查询名字中含有「风」字的学生信息

	SELECT * FROM student WHERE Sname LIKE '%风%';

23. 查询同名同性学生名单，并统计同名人数

	SELECT * FROM student AS t1 INNER JOIN student AS t2 ON t1.Sname = t2.Sname AND t1.SId != t2.Sid;
	SELECT COUNT(1) AS totalCount, Sname FROM student GROUP BY Sname HAVING COUNT(1) > 1;

24. 查询 1990 年出生的学生名单

	SELECT * FROM student WHERE Sage >= '1990-01-01' AND sage <= '1990-12-31';

25. 查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列

	SELECT CId, AVG(score) AS avgScore FROM sc GROUP BY CId ORDER BY AVG(score) DESC, CId ASC;

26. 查询平均成绩大于等于 85 的所有学生的学号、姓名和平均成绩

	SELECT SId, AVG(score) AS avgScore FROM sc GROUP BY SId HAVING AVG(score) >= 85;
	SELECT student.*, t1.avgScore FROM student INNER JOIN (SELECT SId, AVG(score) AS avgScore FROM sc GROUP BY SId HAVING AVG(score) >= 85) AS t1 ON student.SId = t1.SId;

27. 查询课程名称为「数学」，且分数低于 60 的学生姓名和分数

	SELECT CId FROM course WHERE Cname = '数学';
	SELECT SId, score FROM sc WHERE CId IN(SELECT CId FROM course WHERE Cname = '数学') AND score < 60;
	SELECT student.*, t1.score FROM student INNER JOIN (SELECT SId, score FROM sc WHERE CId IN(SELECT CId FROM course WHERE Cname = '数学') AND score < 60) AS t1 ON student.SId = t1.SId;

28. 查询所有学生的课程及分数情况（存在学生没成绩，没选课的情况）

	SELECT t1.SId, t1.score, t2.Cname FROM sc AS t1 INNER JOIN course AS t2 ON t1.CId = t2.CId;
	SELECT t1.*, t2.Cname, t2.score FROM student AS t1 LEFT JOIN (SELECT t1.SId, t1.score, t2.Cname FROM sc AS t1 INNER JOIN course AS t2 ON t1.CId = t2.CId) AS t2 ON t1.SId = t2.SId;

29. 查询任何一门课程成绩在 70 分以上的姓名、课程名称和分数

	SELECT t1.*, t2.Cname, t2.score FROM student AS t1 INNER JOIN (SELECT t1.SId, t1.score, t2.Cname FROM sc AS t1 INNER JOIN course AS t2 ON t1.CId = t2.CId WHERE t1.score >= 70) AS t2 ON t1.SId = t2.SId;

30. 查询不及格的课程

	SELECT t1.*, t2.Cname, t2.score FROM student AS t1 INNER JOIN (SELECT t1.SId, t1.score, t2.Cname FROM sc AS t1 INNER JOIN course AS t2 ON t1.CId = t2.CId WHERE t1.score < 60) AS t2 ON t1.SId = t2.SId;

31. 查询课程编号为 01 且课程成绩在 80 分以上的学生的学号和姓名

	SELECT * FROM student WHERE SId IN (SELECT SId FROM sc WHERE CId = '01' AND score >= 80);

32. 求每门课程的学生人数

	SELECT CId, COUNT(1) AS totalCount FROM sc GROUP BY CId;

33. 成绩不重复，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩

	SELECT TId FROM teacher WHERE Tname = '张三';
	SELECT CId FROM course WHERE TId = (SELECT TId FROM teacher WHERE Tname = '张三');
	SELECT * FROM sc WHERE CId = (SELECT CId FROM course WHERE TId = (SELECT TId FROM teacher WHERE Tname = '张三'));
	SELECT *, RANK() OVER(ORDER BY score DESC) AS ranking FROM sc WHERE CId = (SELECT CId FROM course WHERE TId = (SELECT TId FROM teacher WHERE Tname = '张三'));
	
	SELECT SId, score FROM (
		SELECT *, RANK() OVER(ORDER BY score DESC) AS ranking FROM sc WHERE CId = (SELECT CId FROM course WHERE TId = (SELECT TId FROM teacher WHERE Tname = '张三'))
	) AS t1 WHERE ranking = 1;
	
	SELECT s.*, t2.* FROM student AS s INNER JOIN (
		SELECT SId, score FROM (
			SELECT *, RANK() OVER(ORDER BY score DESC) AS ranking FROM sc WHERE CId = (SELECT CId FROM course WHERE TId = (SELECT TId FROM teacher WHERE Tname = '张三'))
		) AS t1 WHERE ranking = 1
	) AS t2 ON s.SId = t2.SId;

34. 成绩有重复的情况下，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩

	SELECT *, DENSE_RANK() OVER(ORDER BY score DESC) AS ranking FROM sc WHERE CId = (SELECT CId FROM course WHERE TId = (SELECT TId FROM teacher WHERE Tname = '张三'));
	
	SELECT SId, score FROM (
		SELECT *, DENSE_RANK() OVER(ORDER BY score DESC) AS ranking FROM sc WHERE CId = (SELECT CId FROM course WHERE TId = (SELECT TId FROM teacher WHERE Tname = '张三'))
	) AS t1 WHERE ranking = 1;
	
	SELECT s.*, t2.* FROM student AS s INNER JOIN (
		SELECT SId, score FROM (
			SELECT *, DENSE_RANK() OVER(ORDER BY score DESC) AS ranking FROM sc WHERE CId = (SELECT CId FROM course WHERE TId = (SELECT TId FROM teacher WHERE Tname = '张三'))
		) AS t1 WHERE ranking = 1
	) AS t2 ON s.SId = t2.SId;

35. 查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩

	SELECT * FROM sc;
	SELECT s1.*, s2.* FROM sc AS s1 INNER JOIN sc AS s2 ON s1.score = s2.score ORDER BY s1.CId DESC, s1.SId ASC;
	SELECT s1.*, s2.* FROM sc AS s1 INNER JOIN sc AS s2 ON s1.score = s2.score AND s1.SId != s2.SId AND s1.CId != s2.CId ORDER BY s1.CId DESC, s1.SId ASC;

36. 查询每门功成绩最好的前两名

	SELECT *, DENSE_RANK() OVER (PARTITION BY CId ORDER BY score DESC) AS ranking FROM sc ORDER BY CId ASC, SCORE DESC;
	SELECT * FROM (SELECT *, DENSE_RANK() OVER (PARTITION BY CId ORDER BY score DESC) AS ranking FROM sc ORDER BY CId ASC, SCORE DESC) AS t WHERE t.ranking <= 2;

37. 统计每门课程的学生选修人数（超过 5 人的课程才统计）。

	SELECT CId FROM sc GROUP BY CId HAVING COUNT(1) > 5;
	SELECT COUNT(1) AS counting, CId FROM sc GROUP BY CId HAVING counting > 5;

38. 检索至少选修两门课程的学生学号

	SELECT SId FROM sc GROUP BY SId HAVING COUNT(1) >= 2;
	SELECT COUNT(1) AS counting, SId FROM sc GROUP BY SId HAVING counting >= 2;

39. 查询选修了全部课程的学生信息

	SELECT SUM(1) FROM course;
	SELECT SId FROM sc GROUP BY SId HAVING COUNT(1) >= 3;
	SELECT SId FROM sc GROUP BY SId HAVING COUNT(1) = (SELECT SUM(1) FROM course);
	SELECT * FROM student WHERE SId IN(SELECT SId FROM sc GROUP BY SId HAVING COUNT(1) = (SELECT SUM(1) FROM course));

40. 查询各学生的年龄，只按年份来算

	SELECT *, YEAR(Sage) AS birthYear FROM student;
	SELECT *, YEAR(Sage) AS birthYear , YEAR(NOW()) AS nowYear FROM student;
	SELECT *, YEAR(Sage) AS birthYear , YEAR(NOW()) AS nowYear, (YEAR(NOW()) - YEAR(Sage)) AS studentAge FROM student;

41. 按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一

	SELECT *, YEAR(Sage) AS birthYear, YEAR(NOW()) AS nowYear, (YEAR(NOW()) - YEAR(Sage)) AS studentAge,  NOW() AS nowDate FROM student;

	SELECT *, DATE_ADD(Sage, INTERVAL studentAge YEAR) AS nowBirthday FROM (
		SELECT *, YEAR(Sage) AS birthYear, YEAR(NOW()) AS nowYear, (YEAR(NOW()) - YEAR(Sage)) AS studentAge,  NOW() AS nowDate FROM student
	) AS t1;
	
	SELECT *, IF(nowDate < nowBirthday, studentAge - 1, studentAge) AS realStudentAge FROM (
		SELECT *, DATE_ADD(Sage, INTERVAL studentAge YEAR) AS nowBirthday FROM (
			SELECT *, YEAR(Sage) AS birthYear, YEAR(NOW()) AS nowYear, (YEAR(NOW()) - YEAR(Sage)) AS studentAge,  NOW() AS nowDate FROM student
		) AS t1
	) AS t2;

42. 查询本周过生日的学生

SELECT * FROM student WHERE YEARWEEK(DATE_ADD(Sage, INTERVAL (YEAR(NOW()) - YEAR(Sage)) YEAR)) = YEARWEEK(NOW());

43. 查询下周过生日的学生

	SELECT * FROM student WHERE YEARWEEK(DATE_ADD(Sage, INTERVAL (YEAR(NOW()) - YEAR(Sage)) YEAR)) = (YEARWEEK(NOW()) + 1);

44. 查询本月过生日的学生

	SELECT * FROM student WHERE MONTH(Sage) = MONTH(NOW());

45. 查询下月过生日的学生

	SELECT * FROM student WHERE MONTH(Sage) = (MONTH(NOW()) + 1);