MySQL練習題及答案（復習）

新建一個叫做 review 的數據庫，將測試數據腳本導進去。（可以使用Navicat查詢功能）

/*
Navicat MySQL Data Transfer

Source Server         : DB
Source Server Version : 50723
Source Host           : localhost:3306
Source Database       : review

Target Server Type    : MYSQL
Target Server Version : 50723
File Encoding         : 65001

Date: 2019-02-25 23:48:25
*/

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for class
-- ----------------------------
DROP TABLE IF EXISTS `class`;
CREATE TABLE `class` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` char(4) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of class
-- ----------------------------
INSERT INTO `class` VALUES ('1', '高三1班');
INSERT INTO `class` VALUES ('2', '高三2班');
INSERT INTO `class` VALUES ('3', '高三3班');

-- ----------------------------
-- Table structure for course
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` char(8) NOT NULL,
  `teacher_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `name` (`name`),
  KEY `fk_cou_tea` (`teacher_id`),
  CONSTRAINT `fk_cou_tea` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of course
-- ----------------------------
INSERT INTO `course` VALUES ('1', 'python', '1');
INSERT INTO `course` VALUES ('2', 'java', '2');
INSERT INTO `course` VALUES ('3', 'php', '3');
INSERT INTO `course` VALUES ('4', 'c', '1');

-- ----------------------------
-- Table structure for score
-- ----------------------------
DROP TABLE IF EXISTS `score`;
CREATE TABLE `score` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `student_id` int(11) DEFAULT NULL,
  `course_id` int(11) DEFAULT NULL,
  `mark` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fk_sco_stu` (`student_id`),
  KEY `fk_sco_cou` (`course_id`),
  CONSTRAINT `fk_sco_cou` FOREIGN KEY (`course_id`) REFERENCES `course` (`id`),
  CONSTRAINT `fk_sco_stu` FOREIGN KEY (`student_id`) REFERENCES `student` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=18 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of score
-- ----------------------------
INSERT INTO `score` VALUES ('1', '1', '2', '79');
INSERT INTO `score` VALUES ('2', '2', '1', '58');
INSERT INTO `score` VALUES ('3', '2', '3', '66');
INSERT INTO `score` VALUES ('4', '2', '4', '80');
INSERT INTO `score` VALUES ('5', '3', '1', '63');
INSERT INTO `score` VALUES ('6', '3', '4', '95');
INSERT INTO `score` VALUES ('7', '4', '2', '88');
INSERT INTO `score` VALUES ('8', '4', '3', '62');
INSERT INTO `score` VALUES ('9', '5', '2', '59');
INSERT INTO `score` VALUES ('10', '5', '4', '100');
INSERT INTO `score` VALUES ('11', '1', '1', '55');
INSERT INTO `score` VALUES ('12', '3', '2', '81');
INSERT INTO `score` VALUES ('13', '4', '4', '50');
INSERT INTO `score` VALUES ('14', '5', '3', '77');
INSERT INTO `score` VALUES ('15', '1', '4', '58');
INSERT INTO `score` VALUES ('16', '1', '3', '91');
INSERT INTO `score` VALUES ('17', '6', '2', '75');

-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` char(2) NOT NULL,
  `gender` char(1) DEFAULT NULL,
  `class_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fk_cou_cla` (`class_id`),
  CONSTRAINT `fk_cou_cla` FOREIGN KEY (`class_id`) REFERENCES `class` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES ('1', '德瑪', '男', '1');
INSERT INTO `student` VALUES ('2', '妖姬', '女', '2');
INSERT INTO `student` VALUES ('3', '盲僧', '男', '3');
INSERT INTO `student` VALUES ('4', '蜘蛛', '女', '1');
INSERT INTO `student` VALUES ('5', '卡牌', '男', '2');
INSERT INTO `student` VALUES ('6', '露露', '女', '3');

-- ----------------------------
-- Table structure for teacher
-- ----------------------------
DROP TABLE IF EXISTS `teacher`;
CREATE TABLE `teacher` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` char(2) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of teacher
-- ----------------------------
INSERT INTO `teacher` VALUES ('1', '佩奇');
INSERT INTO `teacher` VALUES ('2', '大熊');
INSERT INTO `teacher` VALUES ('3', '路飛');

數據表結構如下圖：

練習題及答案如下：

-- 1、查詢所有的課程的名稱以及對應的任課老師姓名
select course.name as "課程",teacher.name as "任課老師" from course 
left join
teacher
on
course.teacher_id=teacher.id;

------------------------------------------------------------
-- 2、查詢學習課程"python"比課程"java"成績低的學生的學號
select python.student_id from
(select score.student_id,course.name,score.mark from score inner join course on score.course_id=course.id where course.name="python") as python
inner JOIN
(select score.student_id,course.name,score.mark from score inner join course on score.course_id=course.id where course.name="java") as java
on python.student_id=java.student_id
where python.mark<java.mark;

------------------------------------------------------------
-- 3、查詢平均成績大於65分的同學的id和平均成績(保留兩位小數)
select student_id,round(avg(mark),2) as m from score
group by student_id having m>65;

------------------------------------------------------------
-- 4、查詢平均成績大於65分的同學的姓名和平均成績(保留兩位小數);
select student.name,round(avg(mark),2) as m from score
inner join
student
on
score.student_id=student.id
group by student_id having m>65;

------------------------------------------------------------
-- 5、查詢所有同學的姓名、選課數、總成績
select student.name,count(score.course_id) as "選課數",sum(score.mark) as "總成績" from score 
inner join
student
on
score.student_id=student.id
group by student_id;

------------------------------------------------------------
-- 6、查詢沒學過"路飛"老師課的同學的姓名
# 1)"路飛"老師任課的課程id
select course.id from course inner join teacher on course.teacher_id=teacher.id where teacher.name="路飛"
# 2)學過"路飛"老師的課的學生id
select score.student_id from score where score.course_id in
(select course.id from course inner join teacher on course.teacher_id=teacher.id where teacher.name="路飛")
group by score.student_id
# 3)最終結果
select student.name from student where id not in
(select score.student_id from score where score.course_id in
(select course.id from course inner join teacher on course.teacher_id=teacher.id where teacher.name="路飛")
group by score.student_id);

------------------------------------------------------------
-- 7、查詢學過"python"並且也學過"java"課程的同學的姓名
select student.name from score 
left join student on score.student_id=student.id
where
score.course_id=(select id from course where name="python")
or
score.course_id=(select id from course where name="java")
group by score.student_id having count(1)>1;

------------------------------------------------------------
-- 8、查詢學過"路飛"老師所教的全部課程的同學的姓名
select student.name from score inner join student on score.student_id=student.id where score.course_id in
(select course.id from course inner join teacher on course.teacher_id=teacher.id where teacher.name="路飛")
group by score.student_id;

-- 9、查詢有課程成績小於60分的同學的姓名
select name from student where id in
(select student_id from score where mark<60 group by student_id);

------------------------------------------------------------
-- 10、查詢掛科超過兩門(包括兩門)的學生姓名
select name from student where id in
(select student_id from score where mark<60 group by student_id having count(1)>=2);
------------------------------------------------------------
-- 11、查詢選修了全部課程的學生姓名
select name from student where id in
(select student_id from score group by student_id having count(1)=(select count(1) from course));

------------------------------------------------------------
-- 12、查詢至少有一門課程與"卡牌"同學所學課程相同的同學姓名
select name from student where id in
(select student_id from score where course_id in
(select course_id from score inner join student on score.student_id=student.id where student.name="卡牌")
group by student_id)
and name!="卡牌";

------------------------------------------------------------
-- 13、查詢學過"蜘蛛"同學全部課程的其他同學姓名
# 1)"蜘蛛"同學學過的課程id
select course_id from score inner join student on score.student_id=student.id where student.name="蜘蛛"
# 2)score表連student表，並篩選出課程id在（"蜘蛛"同學學過的課程id），並且學生!="蜘蛛"
select student.name from score inner join student on score.student_id=student.id where score.course_id
in (select course_id from score inner join student on score.student_id=student.id where student.name="蜘蛛")
and student.name!="蜘蛛"
# 3)接着對結果進行分組，再次篩選得到最終結果
select student.name from score inner join student on score.student_id=student.id where score.course_id
in (select course_id from score inner join student on score.student_id=student.id where student.name="蜘蛛")
and student.name!="蜘蛛"
group by student_id
having count(1)=(select count(1) from score inner join student on score.student_id=student.id where student.name="蜘蛛");

------------------------------------------------------------
-- 14、查詢和"蜘蛛"同學學習的課程完全相同的其他同學姓名；
# 1)找出與"蜘蛛"學習課程數相同的學生id(你學兩門，我也學兩門)
select * from score where score.student_id 
in
(select student_id from score 
group by score.student_id 
having count(1)=(select count(1) from score inner join student on score.student_id=student.id where student.name="蜘蛛"))
# 2)找出學過"蜘蛛"課程的學生，剩下的一定是至少學過一門"蜘蛛"課程的學生
select * from score where score.student_id 
in
(select student_id from score 
group by score.student_id 
having count(1)=(select count(1) from score inner join student on score.student_id=student.id where student.name="蜘蛛"))
and
score.course_id
in
(select course_id from score inner join student on score.student_id=student.id where student.name="蜘蛛")
# 3)根據學生id進行分組，剩下學生數count(1)=貂蟬學生所學課程數
select student_id from score where score.student_id 
in
(select student_id from score 
group by score.student_id 
having count(1)=(select count(1) from score inner join student on score.student_id=student.id where student.name="蜘蛛"))
and
score.course_id
in
(select course_id from score inner join student on score.student_id=student.id where student.name="蜘蛛")
group by
score.student_id
having count(1)=(select count(1) from score inner join student on score.student_id=student.id where student.name="蜘蛛")
and
score.student_id!=(select id from student where name="蜘蛛")
# 4)最終結果
select name from student where id in
(select student_id from score where score.student_id 
in
(select student_id from score 
group by score.student_id 
having count(1)=(select count(1) from score inner join student on score.student_id=student.id where student.name="蜘蛛"))
and
score.course_id
in
(select course_id from score inner join student on score.student_id=student.id where student.name="蜘蛛")
group by
score.student_id
having count(1)=(select count(1) from score inner join student on score.student_id=student.id where student.name="蜘蛛")
and
score.student_id!=(select id from student where name="蜘蛛"));

------------------------------------------------------------
-- 15、按平均成績倒序顯示所有學生的"python"、"java"、"php"三門的課程成績，按如下形式顯示： 學生id,python,java,php,課程數,平均分
# 1)先查詢單一學生的python課程分數
select mark from score left join course on score.course_id = course.id where course.name = "python" and score.student_id=1;
# 2)將上面查詢的結果作為列字段使用，得到最終結果
select student_id,
(select mark from score left join course on score.course_id = course.id where course.name = "python" and score.student_id=sc.student_id) as "python",
(select mark from score left join course on score.course_id = course.id where course.name = "java" and score.student_id=sc.student_id) as "java",
(select mark from score left join course on score.course_id = course.id where course.name = "php" and score.student_id=sc.student_id) as "php",
count(course_id) as "課程數",
avg(mark) as "平均分"
from score as sc
group by student_id order by avg(mark) desc;

------------------------------------------------------------
-- 16、查詢各科成績最高和最低的分：以如下形式顯示：課程id，最高分，最低分
select course_id,max(mark) as "最高分",min(mark) as "最低分" from score group by course_id;

------------------------------------------------------------
-- 17、統計各科各分數段人數，顯示格式：課程id,課程名稱,[100-85],[85-70],[70-60],[<60]
select course_id,course.name,
sum(case when mark between 85 and 100 then 1 else 0 end) as "[100-85]",
sum(case when mark between 70 and 85 then 1 else 0 end) as "[85-70]",
sum(case when mark between 60 and 70 then 1 else 0 end) as "[70-60]",
sum(case when mark < 60 then 1 else 0 end) as "[<60]"
from score
inner join course
on score.course_id=course.id
GROUP BY score.course_id;

------------------------------------------------------------
-- 18、查詢每門課程名字及其被選修的次數
select course.name,count(1) from score 
inner join course on score.course_id=course.id
group by course_id;

------------------------------------------------------------
-- 19、查詢只選修了一門課程的學生的學號和姓名
select student_id,student.name from score
inner join student on score.student_id=student.id
group by student_id having count(course_id)=1;

------------------------------------------------------------
-- 20、查詢學生表中男生、女生各有多少人
select
sum(case when gender="男" then 1 else 0 end) as "男生",
sum(case when gender="女" then 1 else 0 end) as "女生"
from student

------------------------------------------------------------
-- 21、查詢每門課程的平均成績，結果按平均成績升序排列，平均成績相同時，按課程id降序排列
select course.name,avg(mark) from score
inner join course on score.course_id=course.id
group by course_id
order by avg(mark) asc,course_id desc;

------------------------------------------------------------
-- 22、查詢課程名稱為"python"且分數低於60的學生姓名和分數
select student.name,mark from score
inner join student on score.student_id=student.id
where mark<60 and course_id=(select id from course where name="python");

------------------------------------------------------------
-- 23、求選了課程的學生人數
# 方式一：
select count(distinct student_id) from score;
# 方式二：
select count(1) from (select count(student_id) from score group by student_id) as a;