文章目錄

一、模型

二、表操作

1、創建表結構

CREATE TABLE `dept` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `dept_name` varchar(32),
  PRIMARY KEY (`id`)
) ;

CREATE TABLE `teacher` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(32) ,
  `dept_id` int(11) ,
  PRIMARY KEY (`id`),
  FOREIGN KEY (`dept_id`) REFERENCES `dept` (`id`)
) ;

CREATE TABLE `course` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `course_name` varchar(32) ,
  `teacher_id` int(11),
  PRIMARY KEY (`id`),
  FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`id`)
) ;

CREATE TABLE `students` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(32) ,
  `gender` tinyint(4)  COMMENT '0:male,1:female',
  `birthday` date ,
  `dept_id` int(11),
  PRIMARY KEY (`id`),
  FOREIGN KEY (`dept_id`) REFERENCES `dept` (`id`)
) ;

CREATE TABLE `score` (
  `sid` int(11),
  `course_id` int(11) ,
  `score` tinyint(4),
  FOREIGN KEY (`course_id`) REFERENCES `course` (`id`),
  FOREIGN KEY (`sid`) REFERENCES `students` (`id`)
) ;

2、插入測試數據

INSERT INTO `dept` VALUES (1,'Education'),(2,'Computer Science'),(3,'Mathematics');

INSERT INTO `teacher` VALUES (1,'Zhang san',1),(2,'Li si',1),(3,'Wang wu',2),(4,'Liu liu',3),(5,'Ding \nqi',3),(6,'Zhang yang',2);

INSERT INTO `course` VALUES (1,'math',3),(2,'english',2),(3,'chinese',4),(4,'history',1),(5,'biology',5),(6,'physical',2);

INSERT INTO `students` VALUES (1,'Andrew',0,'1985-08-05',1),(2,'Andy',0,'1983-02-09',1),(3,'Bob',0,'1983-01-03',1),(4,'Ruth',1,'1984-12-23',2),(5,'Mike',0,'1985-01-02',2),(6,'John',0,'1984-02-23',3),(7,'Cindy',1,'1984-12-04',3),(8,'Susan',1,'1983-11-11',3),(9,'John',1,'1984-09-18',2),(10,'Esther',1,'1988-12-25',3);

INSERT INTO `score` VALUES (1,1,56),(1,2,90),(1,3,82),(1,5,56),(2,2,78),(2,4,92),(2,3,77),(2,5,65),(3,1,48),(3,2,95),(3,3,75),(3,4,89),(3,5,92),(4,3,78),(4,4,67),(5,1,75),(5,3,90),(5,4,82),(6,2,58),(6,4,88),(7,1,46),(7,2,65),(7,3,63),(7,4,68),(7,5,32),(8,4,88),(8,5,100),(1,6,76),(2,6,54),(4,6,98),(5,6,87),(8,6,76),(9,1,90),(9,2,59),(10,3,67);

三、練習題

1、查詢85年之後出生的學生人數

SELECT COUNT(*) FROM `students` WHERE `birthday` >'1985-01-01'

2、查詢名字相同的學生名單和個數

SELECT `name`, COUNT(*) FROM `students` GROUP BY `name`

3、將所有學生姓名中前後的空格去掉、
```
SELECT TRIM(`name`) FROM `students`
```

4 、查看每門課程被選修的學生數

SELECT `course_id`,COUNT(`sid`) FROM `score` GROUP BY `course_id`

5、查詢姓zhang的老師的個數

SELECT COUNT(*) FROM `teacher` WHERE SUBSTRING_INDEX(`name`,' ',1) = 'Zhang'

6 、將所有老師的名字拆分成姓和名兩個字段顯示

SELECT
  SUBSTRING(`name`, 1, LOCATE(' ', `name`)) '姓', -- locate()返回子串位置
  SUBSTRING_INDEX(`name`, ' ', - 1) '名' -- 推薦使用SUBSTRING_INDEX()
FROM
  `teacher`

7、把所有學生的生日格式轉換成年月日的格式，並計算每個學生年齡

SELECT
  `name`,
  DATE_FORMAT(`birthday`, '%Y%m%d'),
  FLOOR(DATEDIFF(NOW(), `birthday`) / 365) '年齡'
FROM
  `students`

8、查詢有不及格學生的課程和不及格學生個數

SELECT
  b.`course_name`,
  COUNT(*)
FROM
  `score` a
  JOIN `course` b
    ON a.`course_id` = b.`id`
WHERE a.`score` < 60
GROUP BY a.`course_id`

9、查詢每門課程的平均成績，按升序排序，如果平均成績相同按課程ID降序排序

SELECT
  b.`course_name`,
  AVG(a.`score`)
FROM
  `score` a
  JOIN `course` b
    ON a.`course_id` = b.`id`
GROUP BY a.`course_id`
ORDER BY AVG(a.`score`),a.`course_id` DESC

10、查詢有學生的單科成績小於60的姓名和課程名稱

SELECT
  b.`name`,
  c.`course_name`
FROM
  `score` a
  JOIN `students` b
    ON a.`sid` = b.`id`
  JOIN `course` c
    ON a.`course_id` = c.`id`
WHERE a.`score` < 60

11、查看平均成績大於等於60的所有學生的姓名和平均成績

SELECT
  any_value (b.`name`),
  AVG(a.`score`)
FROM
  `score` a
  JOIN `students` b
    ON a.`sid` = b.`id`
GROUP BY b.`id`
HAVING AVG(a.`score`) > 60

12、將所有學生的考試成績展示爲課程名：成績樣式

SELECT
  a.`sid`,
  CONCAT(b.`course_name`, ':', a.`score`)
FROM
  `score` a
  JOIN `course` b
    ON a.`course_id` = b.`id`

13、查詢不同老師所教不同課程平均分從高到低

SELECT
  b.`teacher_id`,
  b.`id` -- 課程ID
FROM
  `score` a
  JOIN `course` b
    ON a.`course_id` = b.`id`
GROUP BY b.`teacher_id`, b.`id`
ORDER BY AVG(a.`score`) DESC

14、查詢英語課程成績排名第3到第5位的學生姓名和成績

SELECT
  b.`name`,
  a.`score`
FROM
  `score` a
  JOIN `students` b
    ON a.`sid` = b.`id`
  JOIN `course` c
    ON a.`course_id` = c.`id`
WHERE c.`course_name` = 'english'
ORDER BY a.`score` DESC
LIMIT 2, 3

15、查詢所有同學的學號，姓名，選課數和總成績

SELECT
  a.`sid`,
  b.`name`,
  COUNT(a.`course_id`),
  SUM(a.`score`)
FROM
  `score` a
  JOIN `students` b
    ON a.`sid` = b.`id`
GROUP BY b.`id`

16、查詢各科成績中的最高分和最低分

SELECT
  b.`course_name`,
  MAX(a.`score`),
  MIN(a.`score`)
FROM
  `score` a
  JOIN `course` b
    ON a.`course_id` = b.`id`
GROUP BY b.`course_name`

17、計算各科平均成績和及格率百分比

SELECT
  b.`course_name`,
  AVG(a.`score`),
  SUM(IF(a.`score`>=60,1,0))/COUNT(*)
FROM
  `score` a
  JOIN `course` b
    ON a.`course_id` = b.`id`
GROUP BY b.`course_name`

18、查看只學習了一門課程的學生的姓名和學號

SELECT
  `id`,
  `name`
FROM
  `students`
WHERE `id` = (SELECT `sid` FROM `score` GROUP BY `sid` HAVING COUNT(`course_id`)=1)

19、查詢沒學過zhangsan老師課程的學生的學號和姓名

SELECT
  `id`,
  `name`
FROM
  `students`
WHERE `id` NOT IN
  (SELECT DISTINCT
    a.`sid`
  FROM
    `score` a
    JOIN `course` b
      ON a.`course_id` = b.`id`
    JOIN `teacher` c
      ON b.`teacher_id` = c.`id`
  WHERE c.`name` = 'Zhang san')

20、查詢既學過英語也學過語文的學生的學號和姓名

SELECT
  b.`id`,
  b.`name`,
  GROUP_CONCAT(c.`course_name`)
FROM
  `score` a
  JOIN `students` b
    ON a.`sid` = b.`id`
  JOIN `course` c
    ON a.`course_id` = c.`id`
WHERE c.`course_name` IN ('english', 'chinese')
GROUP BY b.`id`
HAVING COUNT(*) >1

21、按平均成績從高到低顯示所有學生的姓名和語文，數學，英語三科成績

SELECT
  any_value(b.`name`),
  SUM(CASE WHEN c.`course_name`='chinese' THEN a.score ELSE 0 END) 'chinese',
  SUM(IF(c.`course_name`='math',a.`score`,0)) 'math',
  SUM(IF(c.`course_name`='english',a.`score`,0)) 'english'
FROM
  `score` a
  JOIN `students` b
    ON a.`sid` = b.`id`
  JOIN `course` c
    ON a.`course_id` = c.`id`
GROUP BY a.`sid`
ORDER BY AVG(a.`score`) DESC

22、統計按照各科成績，分段統計每個課程在90分以上、80-90的、60~80、低於60分的人數

SELECT
  b.`course_name`,
  SUM(IF(a.`score`>=90,1,0)) '90分以上',
  SUM(IF(a.`score`<90 AND a.`score`>=80,1,0)) '80~90分',
  SUM(IF(a.`score`<80 AND a.`score`>=60,1,0)) '60~80分',
  SUM(IF(a.`score`<60,1,0)) '不及格'
FROM
  `score` a
  JOIN `course` b
    ON a.`course_id` = b.`id`
GROUP BY b.`course_name`

23、查看所有英語成績超過數學成績的學生的學號和姓名

SELECT
  a.`id`,a.`name`,c.`score`, b.`score` 
FROM
  `students` a
  JOIN (SELECT a.`sid`,a.`score` FROM `score` a JOIN `course` b ON a.`course_id` = b.`id` WHERE b.`course_name` = 'math') b
    ON a.`id` = b.`sid`
  JOIN (SELECT a.`sid`,a.`score` FROM `score` a JOIN `course` b ON a.`course_id` = b.`id` WHERE b.`course_name` = 'english') c  
    ON a.`id` = c.`sid`
WHERE c.`score`> b.`score`

MySQL之SQL訓練（一）

文章目錄

一、模型

二、表操作

三、練習題

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