-- 1、创建student和score表语句
CREATE TABLE t_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 t_score(
id INT(10) PRIMARY KEY AUTO_INCREMENT,
stu_id INT(10) NOT NULL,
c_name VARCHAR(20),
grade INT(10)
);
INSERT INTO t_student VALUES( 901,'张老大', '男',1985,'计算机系', '北京市海淀区');
INSERT INTO t_student VALUES( 902,'张老二', '男',1986,'中文系', '北京市昌平区');
INSERT INTO t_student VALUES( 903,'张三', '女',1990,'中文系', '湖南省永州市');
INSERT INTO t_student VALUES( 904,'李四', '男',1990,'英语系', '辽宁省阜新市');
INSERT INTO t_student VALUES( 905,'王五', '女',1991,'英语系', '福建省厦门市');
INSERT INTO t_student VALUES( 906,'王六', '男',1988,'计算机系', '湖南省衡阳市');
INSERT INTO t_score VALUES(NULL,901, '计算机',98);
INSERT INTO t_score VALUES(NULL,901, '英语', 80);
INSERT INTO t_score VALUES(NULL,902, '计算机',65);
INSERT INTO t_score VALUES(NULL,902, '中文',88);
INSERT INTO t_score VALUES(NULL,903, '中文',95);
INSERT INTO t_score VALUES(NULL,904, '计算机',70);
INSERT INTO t_score VALUES(NULL,904, '英语',92);
INSERT INTO t_score VALUES(NULL,905, '英语',94);
INSERT INTO t_score VALUES(NULL,906, '计算机',90);
INSERT INTO t_score VALUES(NULL,906, '英语',85);
-- 2、查询student表的所有记录
SELECT * FROM t_student;
-- 3、查询student表的第2条到4条记录
SELECT * FROM t_student LIMIT 1,3;
SELECT * FROM t_student LIMIT 1,3;
-- 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 t_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 t_student WHERE department IN ('计算机系' OR '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 t_student WHERE YEAR(NOW())-birth BETWEEN 28 AND 32;
-- 7、从student表中查询每个院系有多少人
SELECT department,COUNT(id) FROM t_student GROUP BY department;
-- 8、从score表中查询每个科目的最高分
SELECT c_name,MAX(grade) FROM t_score GROUP BY c_name;
-- 9、查询李四的考试科目（c_name）和考试成绩（grade）
SELECT s.name,sc.c_name,sc.grade
FROM t_student AS s
LEFT JOIN t_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 t_student AS s
LEFT JOIN t_score AS sc
ON s.id=sc.stu_id
-- 11、计算每个学生的总成绩
SELECT s.name,SUM(grade)
FROM t_student AS s
LEFT JOIN t_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)
FROM t_student AS s
LEFT JOIN t_score AS sc
ON s.id=sc.stu_id
GROUP BY sc.c_name;
-- 13、查询计算机成绩低于95的学生信息
SELECT *
FROM t_student AS s
LEFT JOIN t_score AS sc
ON s.id=sc.stu_id
WHERE sc.grade<=95 AND sc.c_name='计算机';
-- 14、查询同时参加计算机和英语考试的学生的信息
-- 第一种
SELECT *
FROM t_student
WHERE id IN
(SELECT stu_id
FROM t_score
WHERE c_name = '计算机' OR c_name = '英语'
GROUP BY stu_id
HAVING COUNT(*) = 2);
-- 第二种
SELECT *
FROM t_student
WHERE id IN
(SELECT stu_id
FROM t_score
WHERE stu_id
IN(SELECT stu_id FROM t_score WHERE c_name = '计算机') AND c_name = '英语');
-- 第三种
SELECT s.*
FROM t_student AS s, t_score AS b ,t_score AS c
WHERE s.id = b.stu_id AND b.c_name = '计算机' AND s.id = c.stu_id AND c.c_name = '英语';
-- 第一种
SELECT *
FROM t_student
WHERE id IN
(SELECT stu_id
FROM t_score
WHERE c_name = '计算机' OR c_name = '英语'
GROUP BY stu_id
HAVING COUNT(*) = 2);
-- 第二种
SELECT *
FROM t_student
WHERE id IN
(SELECT stu_id
FROM t_score
WHERE stu_id
IN(SELECT stu_id FROM t_score WHERE c_name = '计算机') AND c_name = '英语');
-- 第三种
SELECT s.*
FROM t_student AS s, t_score AS b ,t_score AS c
WHERE s.id = b.stu_id AND b.c_name = '计算机' AND s.id = c.stu_id AND c.c_name = '英语';
-- 15、将计算机考试成绩按从高到低进行排序
SELECT sc.c_name,sc.grade
FROM t_score AS sc
WHERE sc.c_name='计算机'
ORDER BY sc.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 s.id
FROM t_student AS s
UNION SELECT sc.stu_id
FROM t_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 t_student AS s
LEFT JOIN t_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,YEAR(NOW())-birth AS '年龄',s.department,sc.c_name,sc.grade
FROM t_student AS s
LEFT JOIN t_score AS sc
ON s.id=sc.stu_id
WHERE s.address LIKE '%湖南%';
SELECT s.name,YEAR(NOW())-birth AS '年龄',s.department,sc.c_name,sc.grade
FROM t_student AS s
LEFT JOIN t_score AS sc
ON s.id=sc.stu_id
WHERE s.address LIKE '%湖南%';
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