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MySql连表查询练习 21、查询各科前三名的记录: 笛卡儿积查找 附录-创建测试数据

分类: IT文章 • 2022-07-31 11:40:17

SQL练习

2、查询“生物”课程比“物理”课程成绩高的所有学生的学号；

select * from 
	(select * from score where course_id = 1) as s1
inner join 
	(select * from score where course_id = 2) as s2
on s1.student_id=s2.student_id
	where s1.num>s2.num;

3、查询平均成绩大于60分的同学的学号和平均成绩；

select student_id,avg(num) from score
group by student_id having avg(num) > 60

4、查询所有同学的学号、姓名、选课数、总成绩；

SELECT
	score.student_id,
	student.sname,
	count(course_id),
	sum(score.num)
FROM
	score
LEFT JOIN student ON score.student_id = student.sid
GROUP BY
	score.student_id;

5、查询姓“李”的老师的个数；

select * from teacher where tname like "李%"

6、查询没学过“叶平”老师课的同学的学号、姓名；

select * from student where sid not in ( 
select student_id from score where course_id in (2,4))

7、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；

select student_id,count(1) from score 
where course_id = 1 or course_id=2 
group by student_id

8、查询学过“叶平”老师所教的所有课的同学的学号、姓名；

select student_id, from score 
where course_id in (1,2)  
group by student_id having count(1)=2

9、查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名；

-- 创建两个临时表，用student_id连接起来
SELECT * from 
(select * from score where course_id=2) as s1
left join 
(select * from score where course_id=1) as s2
on s1.student_id = s2.student_id
where s1.num > s2.num

10、查询有课程成绩小于60分的同学的学号、姓名；

select studeny_id from score where num < 60 group by student_id;

11、查询没有学全所有课的同学的学号、姓名；

SELECT * from 
(select * from score where course_id=2) as s1
left join 
(select * from score where course_id=1) as s2
on s1.student_id = s2.student_id
where s1.num > s2.num

12、查询至少有一门课与学号为“001”的同学所学相同的同学的学号和姓名；

select student_id from score where course_id in (1,2,4) group by student_id

14、查询和“002”号的同学学习的课程完全相同的其他同学学号和姓名；

select course_id from score where student_id=2  (1,3,4)


SELECT * from score where course_id in (1,3,4) 
GROUP BY student_id 
having count(1) = 3;


select count(1) from score where student_id=2;

15、删除学习“叶平”老师课的SC表记录；

  delete from score where course_id in (
        select cid from course left join teacher on course.teacher_id = teacher.tid where teacher.name = '叶平'
    )

16、向SC表中插入一些记录，这些记录要求符合以下条件：①没有上过编号“002”课程的同学学号；②插入“002”号课程的平均成绩；

    思路：
        由于insert 支持 
                inset into tb1(xx,xx) select x1,x2 from tb2;
        所有，获取所有没上过002课的所有人，获取002的平均成绩
 
    insert into score(student_id, course_id, num) select sid,2,(select avg(num) from score where course_id = 2)
    from student where sid not in (
        select student_id from score where course_id = 2
    )

17、按平均成绩从低到高显示所有学生的“语文”、“数学”、“英语”三门的课程成绩，按如下形式显示： 学生ID,语文,数学,英语,有效课程数,有效平均分；

select 
    s1.student_id,
    
    (SELECT num from score as s2 where 
    s2.student_id=s1.student_id and s2.course_id=1) as 生物,

    (SELECT num from score as s2 where 
    s2.student_id=s1.student_id and s2.course_id=2) as 物理,

    (SELECT num from score as s2 where 
    s2.student_id=s1.student_id and s2.course_id=3) as 体育,

    (SELECT num from score as s2 where 
    s2.student_id=s1.student_id and s2.course_id=4) as 美术,

    count(1) as 有效数,
    avg(num) as 平均分
from score as s1 GROUP BY student_id

18、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分；

select course_id,max(num),min(num) from score GROUP BY course_id

19、按各科平均成绩从低到高和及格率的百分数从高到低顺序；

select 
course_id,avg(num),
sum(case when num < 60 then 0 else 1 end) as 不及格,
sum(1) as 总人数,
sum(case when num < 60 then 0 else 1 end)/sum(1)
FROM
score group by course_id order by avg(num) desc ;

不考虑成绩并列情况)

查询大于第四名的成绩的学生即可
SELECT * from score left join  
(
select S1.sid,
(select S2.num from score as S2 where S2.course_id=S1.course_id order by S2.num desc LIMIT 1) as first,
(select S2.num from score as S2 where S2.course_id=S1.course_id order by S2.num desc LIMIT 3,1) as four
from score as S1 ) as B
on score.sid=B.sid where score.num > B.four;
select * from score where course_id =1;

考虑并列

select S1.sid,S1.course_id,
(select S2.num from score as S2 where S2.course_id=S1.course_id GROUP BY num order by S2.num desc LIMIT 1) as num1,
(select S2.num from score as S2 where S2.course_id=S1.course_id GROUP BY num order by S2.num desc LIMIT 1,1) as num2,
(select S2.num from score as S2 where S2.course_id=S1.course_id GROUP BY num order by S2.num desc LIMIT 2,1) as num3
from score as S1 GROUP BY course_id;

22、查询每门课程被选修的学生数；

select course_id,count(1) from score 
group by course_id

23、查询出只选修了一门课程的全部学生的学号和姓名；

select student_id,count(1) from score GROUP BY student_id having count(1) = 1;

24、查询男生、女生的人数；

select gender,count(1) from student GROUP BY gender ;

25、查询姓“张”的学生名单；

select sname from student where sname like "张%";

26、查询同名同姓学生名单，并统计同名人数；

select sname from student GROUP BY sname having count(sname) >1;

27、查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列；

select course_id,avg(num) from score GROUP BY course_id ORDER BY avg(num) asc;

28、查询平均成绩大于85的所有学生的学号、姓名和平均成绩；

SELECT student_id,avg(num) from score group by student_id having avg(num)>85

29、查询课程名称为“数学”，且分数低于60的学生姓名和分数；

select student_id from score where course_id = 1 and num <60;

31、求选了课程的学生人数

select course_id,count(1) from score GROUP BY  course_id

32、查询选修“李平老师”老师所授课程的学生中，成绩最高的学生姓名及其成绩；

笛卡儿积查找

34、查询不同课程但成绩相同的学生的学号、课程号、学生成绩

select s1.student_id,s1.course_id,s1.num from score as s1,score as s2 
where s1.sid != s2.sid 
and s1.course_id != s2.course_id 
and s1.num = s2.num

35、查询每门课程成绩最好的前两名；

select 
s1.course_id,
(select num from score as s2 where s2.course_id = s1.course_id ORDER BY num desc limit 1),
(select num from score as s2 where s2.course_id = s1.course_id ORDER BY num desc limit 1,1),
(select num from score as s2 where s2.course_id = s1.course_id ORDER BY num desc limit 2,1)
from score as s1 GROUP BY course_id;

36、检索至少选修两门课程的学生学号；

select student_id from score group by student_id having count(student_id) > 1

37、查询全部学生都选修的课程的课程号和课程名；

select course_id,count(1) from score group by course_id having count(1) = (select count(1) from student);

38、查询没学过“叶平”老师讲授的任一门课程的学生姓名；

select student_id from score where course_id not in (2,4) GROUP by student_id

39、查询两门以上不及格课程的同学的学号及其平均成绩；

 select student_id from  score where num<60 group by student_id HAVING count(1)>=2

40、检索“004”课程分数小于60，按分数降序排列的同学学号；

select * from score where course_id=1 and num <60 order by num desc

41、删除“002”同学的“001”课程的成绩；

delete FROM score where student_id=2 and course = 1;

附录-创建测试数据

在navcat中导入如下测试数据

/*
 Navicat Premium Data Transfer

 Source Server         : localhost
 Source Server Type    : MySQL
 Source Server Version : 50624
 Source Host           : localhost
 Source Database       : sqlexam

 Target Server Type    : MySQL
 Target Server Version : 50624
 File Encoding         : utf-8

 Date: 10/21/2016 06:46:46 AM
*/

SET NAMES utf8;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
--  Table structure for `class`
-- ----------------------------
DROP TABLE IF EXISTS `class`;
CREATE TABLE `class` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `caption` varchar(32) NOT NULL,
  PRIMARY KEY (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `class`
-- ----------------------------
BEGIN;
INSERT INTO `class` VALUES ('1', '三年二班'), ('2', '三年三班'), ('3', '一年二班'), ('4', '二年九班');
COMMIT;

-- ----------------------------
--  Table structure for `course`
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course` (
  `cid` int(11) NOT NULL AUTO_INCREMENT,
  `cname` varchar(32) NOT NULL,
  `teacher_id` int(11) NOT NULL,
  PRIMARY KEY (`cid`),
  KEY `fk_course_teacher` (`teacher_id`),
  CONSTRAINT `fk_course_teacher` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `course`
-- ----------------------------
BEGIN;
INSERT INTO `course` VALUES ('1', '生物', '1'), ('2', '物理', '2'), ('3', '体育', '3'), ('4', '美术', '2');
COMMIT;

-- ----------------------------
--  Table structure for `score`
-- ----------------------------
DROP TABLE IF EXISTS `score`;
CREATE TABLE `score` (
  `sid` int(11) NOT NULL AUTO_INCREMENT,
  `student_id` int(11) NOT NULL,
  `course_id` int(11) NOT NULL,
  `num` int(11) NOT NULL,
  PRIMARY KEY (`sid`),
  KEY `fk_score_student` (`student_id`),
  KEY `fk_score_course` (`course_id`),
  CONSTRAINT `fk_score_course` FOREIGN KEY (`course_id`) REFERENCES `course` (`cid`),
  CONSTRAINT `fk_score_student` FOREIGN KEY (`student_id`) REFERENCES `student` (`sid`)
) ENGINE=InnoDB AUTO_INCREMENT=53 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `score`
-- ----------------------------
BEGIN;
INSERT INTO `score` VALUES ('1', '1', '1', '10'), ('2', '1', '2', '9'), ('5', '1', '4', '66'), ('6', '2', '1', '8'), ('8', '2', '3', '68'), ('9', '2', '4', '99'), ('10', '3', '1', '77'), ('11', '3', '2', '66'), ('12', '3', '3', '87'), ('13', '3', '4', '99'), ('14', '4', '1', '79'), ('15', '4', '2', '11'), ('16', '4', '3', '67'), ('17', '4', '4', '100'), ('18', '5', '1', '79'), ('19', '5', '2', '11'), ('20', '5', '3', '67'), ('21', '5', '4', '100'), ('22', '6', '1', '9'), ('23', '6', '2', '100'), ('24', '6', '3', '67'), ('25', '6', '4', '100'), ('26', '7', '1', '9'), ('27', '7', '2', '100'), ('28', '7', '3', '67'), ('29', '7', '4', '88'), ('30', '8', '1', '9'), ('31', '8', '2', '100'), ('32', '8', '3', '67'), ('33', '8', '4', '88'), ('34', '9', '1', '91'), ('35', '9', '2', '88'), ('36', '9', '3', '67'), ('37', '9', '4', '22'), ('38', '10', '1', '90'), ('39', '10', '2', '77'), ('40', '10', '3', '43'), ('41', '10', '4', '87'), ('42', '11', '1', '90'), ('43', '11', '2', '77'), ('44', '11', '3', '43'), ('45', '11', '4', '87'), ('46', '12', '1', '90'), ('47', '12', '2', '77'), ('48', '12', '3', '43'), ('49', '12', '4', '87'), ('52', '13', '3', '87');
COMMIT;

-- ----------------------------
--  Table structure for `student`
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `sid` int(11) NOT NULL AUTO_INCREMENT,
  `gender` char(1) NOT NULL,
  `class_id` int(11) NOT NULL,
  `sname` varchar(32) NOT NULL,
  PRIMARY KEY (`sid`),
  KEY `fk_class` (`class_id`),
  CONSTRAINT `fk_class` FOREIGN KEY (`class_id`) REFERENCES `class` (`cid`)
) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `student`
-- ----------------------------
BEGIN;
INSERT INTO `student` VALUES ('1', '男', '1', '理解'), ('2', '女', '1', '钢蛋'), ('3', '男', '1', '张三'), ('4', '男', '1', '张一'), ('5', '女', '1', '张二'), ('6', '男', '1', '张四'), ('7', '女', '2', '铁锤'), ('8', '男', '2', '李三'), ('9', '男', '2', '李一'), ('10', '女', '2', '李二'), ('11', '男', '2', '李四'), ('12', '女', '3', '如花'), ('13', '男', '3', '刘三'), ('14', '男', '3', '刘一'), ('15', '女', '3', '刘二'), ('16', '男', '3', '刘四');
COMMIT;

-- ----------------------------
--  Table structure for `teacher`
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
  `tid` int(11) NOT NULL AUTO_INCREMENT,
  `tname` varchar(32) NOT NULL,
  PRIMARY KEY (`tid`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

-- ----------------------------
--  Records of `teacher`
-- ----------------------------
BEGIN;
INSERT INTO `teacher` VALUES ('1', '张磊老师'), ('2', '李平老师'), ('3', '刘海燕老师'), ('4', '朱云海老师'), ('5', '李杰老师');
COMMIT;

SET FOREIGN_KEY_CHECKS = 1;

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