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数据库设计与查询实践：学生成绩管理系统

表结构设计

学生信息表 student_info

字段名称	数据类型	描述
s_number	char(4)	学号，主键
s_name	char(8)	学生姓名
s_sex	char(2)	性别
s_birth	date	出生日期
s_address	varchar(50)	地址

课程信息表 curriculum

字段名称	数据类型	描述
c_number	char(4)	课程编号，主键
c_course	varchar(50)	课程名称
c_credits	int	学分

成绩表 grade

字段名称	数据类型	描述
g_number	char(4)	学号，与课程编号共同作为主键
g_coursenumber	char(4)	课程编号
g_score	int	成绩

1. 查询选修课的人数

SELECT g_coursenumber, COUNT(*) AS students_count
FROM grade
GROUP BY g_coursenumber;

2. 查询学号为0001、0002、0003、0004的学生的姓名和出生日期

SELECT s_name, s_birth
FROM student_info
WHERE s_number IN ('0001', '0002', '0003', '0004');

3. 向grade表插入一条记录，学号为0004、课程编号为0001

INSERT INTO grade (g_number, g_coursenumber, g_score)
VALUES ('0004', '0001', NULL);

4. 查询选课了课程但没有成绩的学生学号和课程编号

SELECT g_number, g_coursenumber
FROM grade
WHERE g_score IS NULL;

5. 删除grade表中分数为空值的记录

DELETE FROM grade
WHERE g_score IS NULL;

6. 查询grade表中分数大于或等于90且课程编号为0001或0002的记录

SELECT *
FROM grade
WHERE g_score >= 90 AND g_coursenumber IN ('0001', '0002');

7. 查询grade表中总分大于400分的学生学号和总分，查询结果按总分升序显示

SELECT g_number, SUM(g_score) AS total_score
FROM grade
GROUP BY g_number
HAVING SUM(g_score) > 400
ORDER BY total_score ASC;

8. 查询grade表中课程编号为0001的课程的学生最高分、最低分及其分数差

SELECT MAX(g_score) AS max_score, MIN(g_score) AS min_score, (MAX(g_score) - MIN(g_score)) AS score_difference
FROM grade
WHERE g_coursenumber = '0001';

9. 统计每个学生的分数都大于70的课程数，查询结果只显示课程数大于或等于3的学生的学号和课程数

SELECT g_number, COUNT(DISTINCT g_coursenumber) AS course_count
FROM grade
WHERE g_score > 70
GROUP BY g_number
HAVING COUNT(DISTINCT g_coursenumber) >= 3;

10. 查询课程平均成绩为80-90的课程编号和平均成绩

SELECT g_coursenumber, AVG(g_score) AS average_score
FROM grade
GROUP BY g_coursenumber
HAVING AVG(g_score) BETWEEN 80 AND 90;