MySQL -数据查询

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2022-04-20

文章目录

一 表的结构

mysql> use mydb;
Database changed
mysql> show tables;
+----------------+
| Tables_in_mydb |
+----------------+
| course         |
| score          |
| student        |
| teacher        |
+----------------+
4 rows in set (0.00 sec)

mysql> select * from course;
+-----+-------+-----+
| cid | cname | tid |
+-----+-------+-----+
| 01  | 语文  | 02  |
| 02  | 数学  | 01  |
| 03  | 英语  | 03  |
+-----+-------+-----+
3 rows in set (0.00 sec)

mysql> select * from score;
+-----+-----+--------+
| sid | cid | sscore |
+-----+-----+--------+
| 01  | 01  |     80 |
| 01  | 02  |     90 |
| 01  | 03  |     99 |
| 02  | 01  |     70 |
| 02  | 02  |     60 |
| 02  | 03  |     80 |
| 03  | 01  |     80 |
| 03  | 02  |     80 |
| 03  | 03  |     80 |
| 04  | 01  |     50 |
| 04  | 02  |     30 |
| 04  | 03  |     20 |
| 05  | 01  |     76 |
| 05  | 02  |     87 |
| 06  | 01  |     31 |
| 06  | 03  |     34 |
| 07  | 02  |     89 |
| 07  | 03  |     98 |
+-----+-----+--------+
18 rows in set (0.00 sec)

mysql> select * from student;
+-----+-------+------------+------+
| sid | sname | sbirth     | ssex |
+-----+-------+------------+------+
| 01  | 赵雷  | 1990-01-01 | 男   |
| 02  | 钱电  | 1990-12-21 | 男   |
| 03  | 孙风  | 1990-05-20 | 男   |
| 04  | 李云  | 1990-08-26 | 女   |
| 05  | 周梅  | 1991-12-01 | 女   |
| 06  | 吴兰  | 1992-03-01 | 女   |
| 07  | 郑竹  | 1989-07-01 | 女   |
| 08  | 王菊  | 1990-01-20 | 女   |
| 09  | 王菊  | 1990-02-20 | 女   |
+-----+-------+------------+------+
9 rows in set (0.00 sec)

mysql> select * from teacher;
+-----+-------+
| tid | tname |
+-----+-------+
| 01  | 张三  |
| 02  | 李四  |
| 03  | 王五  |
+-----+-------+
3 rows in set (0.00 sec)

二 50小题

#01、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
 SELECT st.sid,sname,sbirth,ssex,sc1.sscore
 FROM student st,score sc1,score sc2
 WHERE st.sid=sc1.sid AND 
 sc1.cid='01' AND sc2.cid='02' 
 AND sc1.sscore>sc2.sscore;
 

#02、查询"01"课程比"02"课程成绩低的学生的信息及课程分数
SELECT st.sid,sname,sbirth,ssex,sc1.sscore
FROM student st,score sc1,score sc2
WHERE st.sid=sc1.sid 
AND sc1.cid='01' 
AND sc2.cid='02' 
AND sc1.sscore<sc2.sscore;

#03、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 st.sid,st.sname,ROUND(AVG(sc.sscore),2)
FROM  student st
LEFT JOIN score sc ON sc.sid=st.sid
GROUP BY sc.sid 
HAVING AVG(sc.sscore)>=60;

#04查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩-- (包括有成绩的和无成绩的）
SELECT st.sid,st.sname,ROUND(AVG(sc.sscore),2)
FROM  student st
LEFT JOIN score sc 
ON sc.sid=st.sid
GROUP BY sc.sid 
HAVING AVG(sc.sscore)<60;

#05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
SELECT st.sid,st.sname,COUNT(sc.cid),
CASE WHEN SUM(sc.sscore) IS NULL THEN 0.00 
ELSE ROUND(SUM(sc.sscore),2)  
END AS '总成绩'
FROM student st
LEFT JOIN score sc
ON st.sid=sc.sid
GROUP BY st.sid;

#06 查询"李"姓老师的数量
SELECT COUNT(te.tname)#SELECT COUNT(tname)/SELECT COUNT(*)
FROM teacher te
WHERE tname LIKE"李%";#WHERE tname ="李%"; 失败

#07查询学过"张三"老师授课的同学的信息
SELECT st.*
FROM student st
WHERE st.sid IN
		(SELECT sc.sid 
		FROM score sc 
		WHERE sc.cid
			IN (SELECT c.cid 
			    FROM course c,teacher t 
			    WHERE c.tid=t.tid AND t.tname='张三')); 

#08查询没学过"张三"老师授课的同学的信息
SELECT st.*
FROM student st
WHERE st.sid IN( SELECT sc.sid 
		  FROM score sc 
		  WHERE sc.cid
			IN 
			(SELECT c.cid 
			FROM course c,teacher t 
			WHERE c.tid=t.tid 
			AND t.tname!='张三')
		);

# 09、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息
#方式一：
SELECT st.*
FROM student st
WHERE st.sid IN
		(SELECT sc.sid 
		FROM score sc 
		WHERE sc.sid='01' 
		AND sc.cid='02'); 
 

#10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息
SELECT st.*
FROM student st
WHERE st.sid IN
		(SELECT sc.sid 
		FROM score sc 
		WHERE sc.sid='01' 
		AND sc.cid!='02');  

#11、查询没有学全所有课程的同学的信息
SELECT st.*
FROM student st
LEFT JOIN score sc ON st.sid=sc.sid
GROUP BY st.sid 
HAVING COUNT(sc.sscore)<(
			SELECT COUNT(DISTINCT cid)
			FROM score
			);

#12、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 DISTINCT student.sid,sname 
FROM student,score
WHERE student.sid=score.sid
AND score.cid IN
		(SELECT cid 
		FROM score 
		WHERE sid='01')
 AND  student.sid!='01';

#13、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
#方式一：【有漏洞】如果最多的课程是四门，就不可以使用课程数量相同来判断 
SELECT * FROM student 
WHERE sid IN(
		SELECT DISTINCT sid 
		FROM score 
		WHERE sid NOT IN
				(SELECT sid 
				FROM score 
				WHERE cid NOT IN 
						(SELECT cid 
						 FROM score 
						 WHERE sid='01')
				)
		GROUP BY sid
		HAVING COUNT(cid)=(SELECT COUNT(cid) 
				    FROM score 
				    WHERE sid='01'
				   ) 
AND sid<>'01');

#方式二：
SELECT * 
FROM student 
WHERE sid IN(
	SELECT r2.sid FROM (
			(SELECT sid,cid FROM score WHERE sid="01") AS r1 
			INNER JOIN (
				SELECT sid,cid 
				FROM score 
				WHERE sid IN (
					  SELECT sid FROM score 
					  GROUP BY sid 
					  HAVING sid!="01" 
					  AND COUNT(cid)=(
							SELECT COUNT(cid) 
							FROM score 
							WHERE sid="01")
					     )
				   ) AS r2
	      ON r1.cid=r2.cid)	
			GROUP BY r2.sid 
			HAVING COUNT(r2.sid)=(SELECT COUNT(cid) 
					      FROM score 
					      WHERE sid="01")
		);
#-- 14、查询没学过"张三"老师讲授的任一门课程的学生姓名 
SELECT sname
FROM student
WHERE sid IN (
	SELECT sid 
	FROM score
	WHERE cid IN(
		SELECT cid
		FROM course
		WHERE tid !=(
			SELECT tid
			FROM teacher
			WHERE tname="张三"
			)
		    )
	   );

#-- 15、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 student.sid,student.sname,AVG(sscore)
FROM student, score
WHERE student.sid=score.sid AND sscore<60
GROUP BY student.sid
HAVING COUNT(cid)>=2;
# case when then else end
SELECT student.sid,student.sname,AVG(sscore)
FROM student, score
WHERE student.sid=score.sid 
GROUP BY student.sid
HAVING SUM(CASE WHEN sscore<60 THEN 1 ELSE 0 END)>=2;

#-- 16、检索"01"课程分数小于60，按分数降序排列的学生信息
SELECT *
FROM student st  JOIN
	(SELECT sid,sscore
	 FROM score
	 WHERE cid='01' AND sscore<60) sid
ON st.sid=sid.sid
ORDER BY sid.sscore DESC; 

#-- 17、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 student.sid,
SUM(CASE WHEN cid='01' THEN sscore ELSE NULL END ) cid1,
SUM(CASE WHEN cid='02' THEN sscore ELSE NULL END ) cid2,
SUM(CASE WHEN cid='03' THEN sscore ELSE NULL END ) cid3,
AVG(sscore) average
FROM student,score
WHERE student.sid=score.sid
GROUP BY student.sid
ORDER BY average DESC;

/*-- 18.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 */
#注意如果case when用于count则else必须是NULL不能是0
SELECT score.cid,course.cname,MAX(sscore),MIN(sscore),AVG(sscore),
ROUND( SUM(CASE WHEN sscore>=60 THEN 1 ELSE 0 END)/COUNT(sscore) ,2) '及格率',
ROUND( SUM(CASE WHEN sscore>=70 AND sscore<=80 THEN 1 ELSE 0 END)/COUNT(sscore) ,2) '中等率',
ROUND( SUM(CASE WHEN sscore>80 AND sscore<90 THEN 1 ELSE 0 END)/COUNT(sscore) ,2)'优良率',
ROUND( SUM(CASE WHEN sscore>=90 THEN 1 ELSE 0 END)/COUNT(sscore) ,2)'优秀率'
FROM score,course WHERE score.cid=course.cid
GROUP BY score.cid;

#-- 19、按各科成绩进行排序，并显示排名
/*group by更强调的是一个整体，就是组，
只能显示一个组里满足聚合函数的一条记录， 
partition by 在整体后更强调个体，
能显示组里所有个体的记录*/
SELECT sid, cid,sscore, 
ROW_NUMBER() OVER(PARTITION BY cid ORDER BY sscore DESC) rank_cid
FROM score;

#-- 20、查询学生的总成绩并进行排名
#方式一：
/*自定义变量： 申明变量：SET @crank =0;  
对变量进行赋值：@crank := @crank +1   ，
赋值操作符   =或:=   使用：查找，比较  运算等 ，
作用域：针对于当前会话（连接）有效，作用域同于会话变量*/
SET @crank =0;
SELECT b.sid, b.a, @crank := @crank +1 AS rank1 FROM
					(SELECT sid,SUM(sscore) AS a 
					FROM score 
					GROUP BY sid 
					ORDER BY a DESC) b ;
					
#为什么排序不对？
SET @crank =0;	
SELECT @crank := @crank +1 AS rank1,sc.sid,SUM(sscore) AS a
FROM score sc 
GROUP BY sid 
ORDER BY a DESC;		
		
#方式二：
SELECT st.sid,st.sname,(CASE WHEN SUM(sc.sscore) IS NULL THEN 0 ELSE SUM(sc.sscore) END) AS '总成绩' 
FROM student st
LEFT JOIN score sc 
ON sc.sid=st.sid
GROUP BY st.sid ORDER BY SUM(sc.sscore) DESC;	
				
#-- 21、查询 不同老师所教 不同课程 平均分 从高到低显示
SELECT course.tid,teacher.tname,course.cid,AVG(sscore) average
FROM course,teacher,score
WHERE course.tid=teacher.tid AND course.cid=score.cid
GROUP BY course.tid,course.cid
ORDER BY average DESC;

#-- 22、查询所有课程的成绩第2名到第3名的学生信息及该课程成绩
#简单版：
SELECT sid,sscore FROM
		(SELECT sid, sscore, 
		ROW_NUMBER() OVER(PARTITION BY cid ORDER BY sscore DESC) rank_cid
		FROM score
		) cc
WHERE rank_cid IN (2,3) ;

#升级版：
SELECT st.*,cc.sscore FROM student st,
		(SELECT sid, sscore, 
		ROW_NUMBER() OVER(PARTITION BY cid ORDER BY sscore DESC) rank_cid
		FROM score
		) cc
WHERE rank_cid IN (2,3)AND st.sid=cc.sid ;

#-- 23、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],[0-60]及所占百分比
SELECT score.cid,course.cname,
ROUND( SUM(CASE WHEN  sscore<=100 AND sscore>85 THEN 1 ELSE 0 END)/COUNT(sscore) ,2) '[100-85]百分比',
ROUND( SUM(CASE WHEN sscore>70 AND sscore<85 THEN 1 ELSE 0 END)/COUNT(sscore) ,2)'[85-70]百分比',
ROUND( SUM(CASE WHEN sscore>60 AND sscore<=70 THEN 1 ELSE 0 END)/COUNT(sscore) ,2)'[70-60]百分比',
ROUND( SUM(CASE WHEN sscore<=60 AND sscore>0 THEN 1 ELSE 0 END)/COUNT(sscore) ,2)'[0-60]百分比'
FROM score,course WHERE score.cid=course.cid
GROUP BY score.cid;

#-- 25、查询各科成绩前三名的记录
SELECT cid,
SUM(CASE WHEN rank_cid=1 THEN sscore ELSE NULL END) 'first',
SUM(CASE WHEN rank_cid=2 THEN sscore ELSE NULL END) '2nd',
SUM(CASE WHEN rank_cid=3 THEN sscore ELSE NULL END) '3rd'
FROM (
	SELECT cid,sid,sscore, 
	ROW_NUMBER() OVER (PARTITION BY cid ORDER BY sscore DESC) rank_cid 
	FROM score
     ) cc
GROUP BY cid;

#-- 26、查询每门课程被选修的学生数 
SELECT cid,COUNT(sid)
FROM score
GROUP BY cid;

#-- 27、查询出只有两门课程的全部学生的学号和姓名 
SELECT st.sid,st.sname
FROM student st,score sc
WHERE st.sid=sc.sid
GROUP BY sc.sid HAVING(COUNT(*)=2);

#-- 28、查询男生、女生人数
#为什么错了？
SELECT COUNT(st1.ssex) "男生人数",COUNT(st2.sid)-COUNT(st1.ssex) "女生人数"
FROM student st1,student st2
WHERE st1.ssex='男'; 

SELECT ssex '性别',COUNT(*) '总人数' 
FROM student
GROUP BY ssex;

#-- 29、查询名字中含有"风"字的学生信息
SELECT *
FROM student
WHERE sname LIKE'%风%';

#-- 30、查询同名同性学生名单，并统计同名人数
SELECT sname,COUNT(*) AS NUM 
FROM student
GROUP BY sname HAVING (COUNT(student.sid)>1);

#-- 31、查询1990年出生的学生名单
#方式一：必须是Y才可以
SELECT *
FROM student
WHERE DATE_FORMAT(sbirth,'%Y')LIKE'1990';

#方式二：
SELECT *
FROM student
WHERE YEAR(sbirth)='1990';

#-- 32、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(sscore)
FROM score
GROUP BY cid
ORDER BY AVG(sscore) DESC,cid ASC;

#-- 33、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 st.sid,st.sname,ROUND( AVG(sscore),2) '平均成绩'
FROM student st ,score sc
WHERE st.sid=sc.sid
GROUP BY sc.sid HAVING(AVG(sscore)>85);

#-- 34、查询课程名称为"数学"，且分数低于60的学生姓名和分数 
SELECT sname,'数学',sc2.sscore
FROM student st,(SELECT *
		FROM score
		WHERE cid=(SELECT cid 
			FROM course 
			WHERE cname='数学')
		AND sscore<60) sc2
WHERE st.sid=sc2.sid ;

#-- 35、查询所有学生的课程及分数情况；
SELECT st.sid,co.cname,sc.sscore
FROM student st , score sc , course co
WHERE st.sid=sc.sid AND sc.cid=co.cid; 

#-- 36、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 sname,cname,sscore
FROM score s 
JOIN course c ON s.cid=c.cid
JOIN Student stu ON s.sid=stu.sid
WHERE sscore>=70;

#-- 37、查询不及格的课程
SELECT DISTINCT(co.cname)
FROM course co JOIN score sc
ON co.cid=sc.cid
WHERE sc.sscore<60;

#-- 38、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 st.sid,sname
FROM student st
JOIN score  sc ON st.sid=sc.sid
WHERE cid='01' AND sscore>=80;

#-- 39、求每门课程的学生人数 
SELECT cid,COUNT(*) '人数'
FROM score
GROUP BY cid;

#-- 40、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 st.*,c.cid,sscore
FROM teacher t JOIN course c ON t.tid=c.tid
JOIN score s ON s.cid = c.cid
JOIN student st ON st.sid = s.sid
WHERE t.tname='张三'
ORDER BY sscore DESC
LIMIT 1;

#-- 41、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 DISTINCT a.sid,a.cid,a.sscore
FROM Score a,Score b
WHERE a.cid<>b.cid AND a.sscore=b.sscore;

#-- 42、查询每门功成绩最好的前两名 
SELECT t1.*
FROM(SELECT cname,
     RANK() OVER(PARTITION BY s.cid ORDER BY sscore DESC) rs,
     stu.*
     FROM score s 
     JOIN student stu ON  s.sid= stu.sid
     JOIN Course c ON c.cid=s.cid
    )t1
WHERE t1.rs <=2;

#-- 43、统计每门课程的学生选修人数（超过5人的课程才统计）。
#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,COUNT(*)
FROM score
GROUP BY cid HAVING(COUNT(*)>5)
ORDER BY COUNT(*) DESC,cid ASC;

#-- 44、检索至少选修两门课程的学生学号 
SELECT sid 
FROM score
GROUP BY sid
HAVING COUNT(*)>=2;
#-- 45、查询选修了全部课程的学生信息 
SELECT * 
FROM student
WHERE sid IN(
	SELECT sid
	FROM score
	GROUP BY sid
	HAVING COUNT(*)=(
			SELECT COUNT(*) 
			FROM course 
			)
	    );
#-- 46、查询各学生的年龄
#-- 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 sname,sbirth,
(DATE_FORMAT(NOW(),'%Y') - DATE_FORMAT(sbirth,'%Y') -
(CASE WHEN DATE_FORMAT(NOW(),'%m%d') > DATE_FORMAT(sbirth,'%m%d') 
THEN 0 ELSE 1 END)
) AS age
FROM student;
#-- 47、查询本周过生日的学生
SELECT * FROM Student
WHERE WEEKOFYEAR(CONCAT(
			DATE_FORMAT(CURRENT_DATE,'%Y'),
			'-',DATE_FORMAT(Sbirth,'%m-%d')
			)
		) = WEEKOFYEAR(CURRENT_DATE);
#-- 48、查询下周过生日的学生
SELECT * FROM Student
WHERE WEEKOFYEAR(CONCAT(
			DATE_FORMAT(CURRENT_DATE,'%Y'),
			'-',DATE_FORMAT(Sbirth,'%m-%d')
			)
		) = WEEKOFYEAR(CURRENT_DATE)+1;

#-- 49、查询本月过生日的学生
SELECT * 
FROM student
WHERE MONTH(sbirth)=MONTH(DATE(NOW()));
#-- 50、查询下月过生日的学生
SELECT * 
FROM student
WHERE MONTH(sbirth)=(MONTH(DATE(NOW()))+1);

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