MySQL数据库操作练习

一、数据库操作（5例）

1. 创建数据库school，指定字符集为utf8mb4

CREATE DATABASE IF NOT EXISTS school CHARACTER SET utf8mb4; 

2. 查看所有数据库

SHOW DATABASES;

3. 切换到school数据库

USE school;

4. 查看当前使用的数据库

SELECT DATABASE();

5. 删除数据库test（若存在）

DROP DATABASE IF EXISTS test;

二、表操作（10例）

6. 创建学生表student（id, name, age, gender）

CREATE TABLE IF NOT EXISTS student (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(50) NOT NULL,
  age INT,
  gender VARCHAR(2)
);

7. 查看student表结构

DESC student;

8. 向student表添加birthday字段（DATE类型）

ALTER TABLE student ADD birthday DATE;

9. 修改student表的age字段为TINYINT

ALTER TABLE student MODIFY age TINYINT;

10. 创建课程表course（id, course_name）

CREATE TABLE course (
  id INT PRIMARY KEY AUTO_INCREMENT,
  course_name VARCHAR(100) NOT NULL
);

11. 创建成绩表score（关联学生和课程）

CREATE TABLE score (
  id INT PRIMARY KEY AUTO_INCREMENT,
  student_id INT,
  course_id INT,
  score INT,
  FOREIGN KEY (student_id) REFERENCES student(id),
  FOREIGN KEY (course_id) REFERENCES course(id)
);

12. 查看school库中所有表

SHOW TABLES;

13. 为student表的name字段添加索引

CREATE INDEX idx_name ON student(name);

14. 复制student表结构到student_backup

CREATE TABLE student_backup LIKE student;

15. 删除student_backup表

DROP TABLE IF EXISTS student_backup;

三、数据插入（10例）

16. 向student表插入1条数据

INSERT INTO student (name, age, gender) VALUES ('张三', 18, '男');

17. 向student表批量插入3条数据

INSERT INTO student (name, age, gender) VALUES 
  ('李四', 19, '女'),
  ('王五', 18, '男'),
  ('赵六', 20, '女');

18. 向course表插入课程

INSERT INTO course (course_name) VALUES ('数学'), ('英语');

19. 向score表插入成绩（学生1选课程1，分数85）

INSERT INTO score (student_id, course_id, score) VALUES (1, 1, 85);

20. 插入成绩时忽略主键冲突

INSERT IGNORE INTO score (id, student_id, course_id, score) VALUES (1, 1, 2, 90);

21. 向student表插入含NULL的记录

INSERT INTO student (name, age) VALUES ('孙七', NULL); -- gender为NULL

22. 复制student表中年龄>18的学生到student_adult

CREATE TABLE student_adult LIKE student;
INSERT INTO student_adult SELECT * FROM student WHERE age > 18;

23. 向score表插入分数为100的数据

INSERT INTO score (student_id, course_id, score) VALUES (2, 1, 100);

24. 批量插入多条成绩

INSERT INTO score (student_id, course_id, score) VALUES 
  (1, 2, 90),
  (3, 1, 76),
  (4, 2, 95);

25. 向student表插入指定id的记录

INSERT INTO student (id, name, age) VALUES (10, '周八', 21);

四、基础查询（20例）

26. 查询student表所有学生的所有信息

SELECT * FROM student;

27. 查询student表中所有学生的姓名和年龄

SELECT name, age FROM student;

28. 查询student表中性别为'男'的学生

SELECT * FROM student WHERE gender = '男';

29. 查询student表中年龄大于18的学生

SELECT * FROM student WHERE age > 18;

30. 查询student表中年龄在18~20之间的学生

SELECT * FROM student WHERE age BETWEEN 18 AND 20;

31. 查询student表中年龄为18或20的学生

SELECT * FROM student WHERE age IN (18, 20);

32. 查询student表中姓名包含'张'的学生

SELECT * FROM student WHERE name LIKE '%张%';

33. 查询student表中姓名以'李'开头的学生

SELECT * FROM student WHERE name LIKE '李%';

34. 查询student表中年龄为空的学生

SELECT * FROM student WHERE age IS NULL;

35. 查询student表中年龄不为空且性别为女的学生

SELECT * FROM student WHERE age IS NOT NULL AND gender = '女';

36. 查询score表中分数大于等于90的记录

SELECT * FROM score WHERE score >= 90;

37. 查询score表中分数在80~90之间的记录

SELECT * FROM score WHERE score > 80 AND score < 90;

38. 查询student表并给列起别名

SELECT name AS '学生姓名', age '年龄' FROM student;

39. 查询student表中所有不重复的年龄

SELECT DISTINCT age FROM student;

40. 查询student表中年龄最大的3位学生

SELECT * FROM student ORDER BY age DESC LIMIT 3;

41. 查询score表中课程ID为2的分数，按分数降序

SELECT * FROM score WHERE course_id = 2 ORDER BY score DESC;

42. 查询student表所有学生，按年龄升序

SELECT * FROM student ORDER BY age;

43. 查询student表，按年龄降序，同年龄按姓名升序

SELECT * FROM student ORDER BY age DESC, name ASC;

44. 查询student表第2~4条数据

SELECT * FROM student LIMIT 1, 3;

45. 查询score表中分数最高的前2名记录

SELECT * FROM score ORDER BY score DESC LIMIT 2;

五、聚合与分组（15例）

46. 统计student表中学生总数

SELECT COUNT(*) AS '学生总数' FROM student;

47. 统计student表中年龄不为NULL的学生数

SELECT COUNT(age) AS '年龄非空人数' FROM student;

48. 计算score表中所有分数的总和

SELECT SUM(score) AS '总分数' FROM score;

49. 计算score表中课程1的平均分

SELECT AVG(score) AS '课程1平均分' FROM score WHERE course_id = 1;

50. 查找score表中的最高分数

SELECT MAX(score) AS '最高分' FROM score;

51. 查找student表中最小的年龄（不含NULL）

SELECT MIN(age) AS '最小年龄' FROM student WHERE age IS NOT NULL;

52. 统计student表中不同性别的人数

SELECT gender, COUNT(*) AS '人数' FROM student GROUP BY gender;

53. 计算每门课程的平均分

SELECT course_id, AVG(score) AS '平均分' FROM score GROUP BY course_id;

54. 统计每个学生的选课数量

SELECT student_id, COUNT(course_id) AS '选课数量' FROM score GROUP BY student_id;

55. 计算每门课程的最高分和最低分

SELECT course_id, MAX(score) AS '最高分', MIN(score) AS '最低分' FROM score GROUP BY course_id;

56. 筛选出平均分大于85的课程

SELECT course_id, AVG(score) AS '平均分' FROM score GROUP BY course_id HAVING 平均分 > 85;

57. 筛选出总分>200的学生

SELECT student_id, SUM(score) AS '总分' FROM score GROUP BY student_id HAVING 总分 > 200;

58. 按性别分组，统计每组的平均年龄

SELECT gender, AVG(age) AS '平均年龄' FROM student WHERE age IS NOT NULL GROUP BY gender;

59. 按课程ID分组，统计选课人数>=2的课程

SELECT course_id, COUNT(student_id) AS '选课人数' FROM score GROUP BY course_id HAVING 选课人数 >= 2;

60. 按学生ID分组，计算最高分，排除分数<60的记录

SELECT student_id, MAX(score) AS '最高分' FROM score WHERE score >= 60 GROUP BY student_id;

六、连接查询（15例）

61. 内连接：查询学生姓名和对应的课程名称（有成绩的）

SELECT s.name, c.course_name 
FROM score sc 
JOIN student s ON sc.student_id = s.id 
JOIN course c ON sc.course_id = c.id

62. 左连接：查询所有学生的姓名及成绩（包括没成绩的）

SELECT s.name, sc.score 
FROM student s 
LEFT JOIN score sc ON s.id = sc.student_id;

63. 右连接：查询所有课程及对应的分数（包括没分数的）

SELECT c.course_name, sc.score 
FROM score sc 
RIGHT JOIN course c ON sc.course_id = c.id;

64. 左连接+筛选：查询没有成绩的学生姓名

SELECT s.name 
FROM student s 
LEFT JOIN score sc ON s.id = sc.student_id 
WHERE sc.id IS NULL;

65. 三表连接：查询学生姓名、课程名称和分数

SELECT s.name, c.course_name, sc.score 
FROM score sc 
JOIN student s ON sc.student_id = s.id 
JOIN course c ON sc.course_id = c.id;

66. 内连接+条件：查询课程名称为'数学'的学生姓名和分数

SELECT s.name, sc.score 
FROM score sc 
JOIN student s ON sc.student_id = s.id 
JOIN course c ON sc.course_id = c.id 
WHERE c.course_name = '数学';

67. 左连接+分组：查询每个学生的姓名及选课数量

SELECT s.name, COUNT(sc.course_id) AS '选课数量' 
FROM student s 
LEFT JOIN score sc ON s.id = sc.student_id 
GROUP BY s.name;

68. 连接查询+排序：按分数降序显示学生、课程和分数

SELECT s.name, c.course_name, sc.score 
FROM score sc 
JOIN student s ON sc.student_id = s.id 
JOIN course c ON sc.course_id = c.id 
ORDER BY sc.score DESC;

69. 自连接：查询年龄相同的学生姓名

SELECT s1.name, s2.name, s1.age 
FROM student s1 
JOIN student s2 ON s1.age = s2.age 
WHERE s1.id < s2.id;

70. 右连接+筛选：查询没有学生选的课程名称

SELECT c.course_name 
FROM score sc 
RIGHT JOIN course c ON sc.course_id = c.id 
WHERE sc.id IS NULL;

71. 内连接+聚合：查询每门课程的名称和平均分

SELECT c.course_name, AVG(sc.score) AS '平均分' 
FROM score sc 
JOIN course c ON sc.course_id = c.id 
GROUP BY c.course_name;

72. 左连接+条件：查询年龄>18的学生姓名及成绩

SELECT s.name, sc.score 
FROM student s 
LEFT JOIN score sc ON s.id = sc.student_id 
WHERE s.age > 18;

73. 连接查询+多条件：查询女生且分数>85的记录

SELECT s.name, c.course_name, sc.score 
FROM score sc 
JOIN student s ON sc.student_id = s.id 
JOIN course c ON sc.course_id = c.id 
WHERE s.gender = '女' AND sc.score > 85;

74. 左连接+计算：查询每个学生的姓名和总分（含0分）

SELECT s.name, IFNULL(SUM(sc.score), 0) AS '总分' 
FROM student s 
LEFT JOIN score sc ON s.id = sc.student_id 
GROUP BY s.name;

75. 连接查询+限制：查询分数最高的3名学生姓名和分数

SELECT s.name, sc.score 
FROM score sc 
JOIN student s ON sc.student_id = s.id 
ORDER BY sc.score DESC 
LIMIT 3;

七、子查询（15例）

76. 子查询在WHERE中：查询与'张三'同年龄的学生

SELECT name FROM student WHERE age = (SELECT age FROM student WHERE name = '张三');

77. 子查询返回多个值：查询选了课程1或2的学生ID

SELECT DISTINCT student_id FROM score WHERE course_id IN (1, 2);

78. 子查询+比较：查询年龄大于平均年龄的学生

SELECT name FROM student WHERE age > (SELECT AVG(age) FROM student WHERE age IS NOT NULL);

79. 派生表：查询每个学生的总分

SELECT student_id, total_score 
FROM (SELECT student_id, SUM(score) AS total_score FROM score GROUP BY student_id) AS s_total;

80. EXISTS子查询：查询选了课程的学生姓名

SELECT name FROM student s WHERE EXISTS (SELECT 1 FROM score sc WHERE sc.student_id = s.id);

81. NOT EXISTS子查询：查询没选任何课程的学生

SELECT name FROM student s WHERE NOT EXISTS (SELECT 1 FROM score sc WHERE sc.student_id = s.id);

82. 子查询+聚合：查询最高分对应的学生和课程ID

SELECT student_id, course_id FROM score WHERE score = (SELECT MAX(score) FROM score);

83. 子查询在SELECT中：查询每个学生的选课数量

SELECT name, (SELECT COUNT(*) FROM score sc WHERE sc.student_id = s.id) AS '选课数量' FROM student s;

84. 多层子查询：查询选了'数学'的学生姓名

SELECT name FROM student WHERE id IN (
  SELECT student_id FROM score WHERE course_id = (
    SELECT id FROM course WHERE course_name = '数学'
  )
);

85. 子查询+ANY：查询分数高于课程1中任何一个分数的记录

SELECT * FROM score WHERE score > ANY (SELECT score FROM score WHERE course_id = 1);

86. 子查询+ALL：查询分数高于课程1中所有分数的记录

SELECT * FROM score WHERE score > ALL (SELECT score FROM score WHERE course_id = 1);

87. 子查询+NOT IN：查询没选课程1的学生ID

SELECT DISTINCT student_id FROM score WHERE student_id NOT IN (
  SELECT student_id FROM score WHERE course_id = 1
);

88. 派生表+连接：查询总分大于200的学生姓名

SELECT s.name 
FROM student s 
JOIN (SELECT student_id, SUM(score) AS total FROM score GROUP BY student_id HAVING total > 200) AS sc_total 
ON s.id = sc_total.student_id;

89. 子查询+多条件：查询年龄比'李四'大且性别相同的学生

SELECT name FROM student 
WHERE age > (SELECT age FROM student WHERE name = '李四') 
AND gender = (SELECT gender FROM student WHERE name = '李四');

90. 子查询+CASE：查询学生姓名及是否及格

SELECT name, 
  (CASE WHEN sc.score >= 60 THEN '及格' ELSE '不及格' END) AS '是否及格' 
FROM student s 
LEFT JOIN score sc ON s.id = sc.student_id;

八、数据修改与删除（10例）

91. 修改student表中'张三'的年龄为19

UPDATE student SET age = 19 WHERE name = '张三';

92. 批量修改：所有学生年龄增加1

UPDATE student SET age = age + 1 WHERE age IS NOT NULL;

93. 修改score表中学生1的课程1分数为90

UPDATE score SET score = 90 WHERE student_id = 1 AND course_id = 1;

94. 修改course表中'数学'的名称为'高等数学'

UPDATE course SET course_name = '高等数学' WHERE course_name = '数学';

95. 修改student表中年龄为NULL的学生，设置为18

UPDATE student SET age = 18 WHERE age IS NULL;

96. 删除student表中姓名为'周八'的记录

DELETE FROM student WHERE name = '周八';

97. 删除score表中学生2的所有成绩

DELETE FROM score WHERE student_id = 2;

98. 删除score表中分数<60的记录

DELETE FROM score WHERE score < 60;

99. 清空score表所有数据（保留表结构）

TRUNCATE TABLE score;

100. 修改student表中'王五'的性别和年龄

UPDATE student SET gender = '女', age = 19 WHERE name = '王五';