第三次作业

分别查询 student 表和 score 表的所有记录

SELECT * FROM student;

SELECT * FROM score;

 查询 student 表的第 2 条到第 5 条记录

SELECT * FROM student LIMIT 1, 4;

. 从 student 表中查询计算机系和英语系的学生的信息

SELECT * FROM student WHERE department = '计算机系' OR department = '英语系';

4. 从 student 表中查询年龄小于 22 岁的学生信息

SELECT * FROM student WHERE 2025 - birth_year < 22;

 从 student 表中查询每个院系有多少人

SELECT department, COUNT(*) AS student_count

FROM student

GROUP BY department;

从 score 表中查询每个科目的最高分

SELECT c_name, MAX(grade) AS max_grade FROM score GROUP BY c_name;

. 用连接的方式查询所有学生的信息和考试信息

SELECT * FROM student st LEFT JOIN score s ON st.id = s.stu_id;

. 计算每个学生的总成绩

SELECT st.id, st.name, SUM(s.grade) AS total_grade FROM student st JOIN score s ON st.id = s.stu_id GROUP BY st.id, st.name;

计算每个考试科目的平均成绩

SELECT c_name, AVG(grade) AS avg_grade FROM score GROUP BY c_name;

1. 查询计算机成绩低于 95 的学生信息

SELECT st.* FROM student st JOIN score s ON st.id = s.stu_id WHERE s.c_name = '计算机' AND s.grade < 95;

 将计算机考试成绩按从高到低进行排序

SELECT * FROM score WHERE c_name = '计算机' ORDER BY grade DESC;

. 从 student 表和 score 表中查询出学生的学号，然后合并查询结果

SELECT id AS stu_id FROM student UNION SELECT stu_id FROM score;

查询姓朱或姓王的同学的姓名、院系和考试科目及成绩

SELECT st.name, st.department, s.c_name, s.grade FROM student st JOIN score s ON st.id = s.stu_id WHERE st.name LIKE '朱%' OR st.name LIKE '王%';

 查询籍贯是湖南的学生的姓名、年龄、院系和考试科目及成绩

SELECT st.name, 2025 - st.birth_year AS age, st.department, s.c_name, s.grade FROM student st JOIN score s ON st.id = s.stu_id WHERE st.address LIKE '湖南省%';