数据库周测汇总

-- 1、创建student和score表语句
CREATE TABLE student(
    id INT(10) PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(20) NOT NULL,
    sex VARCHAR(4),
    birth YEAR,
    department VARCHAR(20) NOT NULL,
    address VARCHAR(50)
);
CREATE TABLE score(
    id INT(10) PRIMARY KEY AUTO_INCREMENT,
    stu_id INT(10) NOT NULL,
    c_name VARCHAR(20),
    grade INT(10)
);
-- 2、查询student表的所有记录
SELECT * FROM student;
-- 3、查询student表的第2条到4条记录
SELECT * from student LIMIT 1,2;
-- 4、从student表查询所有学生的学号（id）、姓名（name）和院系（department）的信息
SELECT id,name,department FROM student;
-- 5、从student表中查询计算机系和英语系的学生的信息（用 IN 关键字）
SELECT * FROM student WHERE department in ('计算机系','英语系');
-- 6、从student表中查询年龄18~22岁的学生信息（用 BETWEEN AND）
SELECT * FROM student WHERE YEAR(NOW()) - birth BETWEEN 18 and 22;
-- 7、从student表中查询每个院系有多少人
SELECT department as '院系', count(*) as '人数'  FROM student GROUP BY department;
-- 8、从score表中查询每个科目的最高分
SELECT c_name,MAX(grade) as '最高分' FROM score GROUP BY c_name;
-- 9、查询李四的考试科目（c_name）和考试成绩（grade）
SELECT sc.c_name,sc.grade FROM student as s LEFT JOIN score as sc ON s.id = sc.stu_id WHERE s.`name`='李四';
-- 10、用连接的方式查询所有学生的信息和考试信息
SELECT * FROM student as s LEFT JOIN score as sc ON s.id = sc. stu_id;
-- 11、计算每个学生的总成绩
SELECT s.name,SUM(sc.grade) as '总成绩' from student as s LEFT JOIN score as sc ON s.id = sc.stu_id GROUP BY s.name;
-- 12、计算每个考试科目的平均成绩
SELECT sc.c_name,avg(grade) as '平均成绩' FROM score as sc GROUP BY sc.c_name;
-- 13、查询计算机成绩低于95的学生信息
SELECT * FROM student as s LEFT JOIN score as sc on s.id=sc.stu_id WHERE c_name='计算机' AND grade < 95;
-- 14、查询同时参加计算机和英语考试的学生的信息*
SELECT * FROM student as s WHERE id in (SELECT stu_id from score as sc
WHERE c_name = '计算机' OR c_name = '英语' GROUP BY stu_id HAVING COUNT(*) = 2);
-- 二
SELECT * FROM student WHERE id IN
(SELECT stu_id FROM score WHERE stu_id IN(SELECT stu_id FROM score WHERE c_name = '计算机') AND c_name = '英语');
-- 15、将计算机考试成绩按从高到低进行排序
SELECT grade FROM score as sc WHERE c_name = '计算机' ORDER BY grade DESC;
-- 16、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 FROM student as s UNION SELECT stu_id FROM score as sc ;
-- 17、查询姓张或者姓王的同学的姓名、院系和考试科目及成绩
SELECT s.name,s.department,sc.c_name,sc.grade FROM student as s
LEFT JOIN score as sc ON s.id = sc.stu_id WHERE s.name LIKE '%张%' OR s.name LIKE '%王%';
-- 18、查询都是湖南的学生的姓名、年龄、院系和考试科目及成绩
SELECT s.name,s.birth,s.department,sc.c_name,sc.grade FROM student as s LEFT JOIN score as sc ON s.id = sc.stu_id WHERE s.address LIKE '湖南%';