MySQL学习（4）多表查询
1.创建student和score表
CREATE TABLE student (
id INT(10) NOT NULL UNIQUE PRIMARY KEY ,
name VARCHAR(20) NOT NULL ,
sex VARCHAR(4) ,
birth YEAR,
department VARCHAR(20) ,
address VARCHAR(50)
);
创建score表。SQL代码如下：
CREATE TABLE score (
id INT(10) NOT NULL UNIQUE PRIMARY KEY AUTO_INCREMENT ,
stu_id INT(10) NOT NULL ,
c_name VARCHAR(20) ,
grade INT(10)
);
2.为student表和score表增加记录
向student表插入记录的INSERT语句如下：
INSERT INTO student VALUES( 901,'张老大', '男',1985,'计算机系', '北京市海淀区');
INSERT INTO student VALUES( 902,'张老二', '男',1986,'中文系', '北京市昌平区');
INSERT INTO student VALUES( 903,'张三', '女',1990,'中文系', '湖南省永州市');
INSERT INTO student VALUES( 904,'李四', '男',1990,'英语系', '辽宁省阜新市');
INSERT INTO student VALUES( 905,'王五', '女',1991,'英语系', '福建省厦门市');
INSERT INTO student VALUES( 906,'王六', '男',1988,'计算机系', '湖南省衡阳市');
向score表插入记录的INSERT语句如下：
INSERT INTO score VALUES(NULL,901, '计算机',98);
INSERT INTO score VALUES(NULL,901, '英语', 80);
INSERT INTO score VALUES(NULL,902, '计算机',65);
INSERT INTO score VALUES(NULL,902, '中文',88);
INSERT INTO score VALUES(NULL,903, '中文',95);
INSERT INTO score VALUES(NULL,904, '计算机',70);
INSERT INTO score VALUES(NULL,904, '英语',92);
INSERT INTO score VALUES(NULL,905, '英语',94);
INSERT INTO score VALUES(NULL,906, '计算机',90);
INSERT INTO score VALUES(NULL,906, '英语',85);
1.查询student表的所有记录
select * from student ;
2.查询student表的第2条到4条记录
查询连续的多行记录(第n~m行)
select * from table1 limit n-1,m-n+1;select * from student limit 1,3;
3.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;
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 = '英语系' or department = ' 计算机系';
5.从student表中查询年龄18~22岁的学生信息
select * from student where birth < 2003 and birth > 1999 ;
简单做个减法 当前时间 - 18 or 22 要注意大小。
6.从student表中查询每个院系有多少人
select department,count(1) from student group by department;
7.从score表中查询每个科目的最高分
select c_name,max(grade) from score group by c_name;
8.查询李四的考试科目（c_name）和考试成绩（grade）
select c_name,grade
-> from score where stu_id=
-> (select id from student
-> where name = '李四');
9.用连接的方式查询所有学生的信息和考试信息
select student.id,name,sex,birth,department,address,c_name,grade from student,score where student.id = score.stu_id;
10.计算每个学生的总成绩
select student.id,name,sum(grade) from student,score where student.idd= score.stu_id group by id;
11.计算每个考试科目的平均成绩
SELECT c_name,AVG(grade) FROM score GROUP BY c_name;
12.查询计算机成绩低于95的学生信息
select * from student where id in (select stu_id from score where c_name ='计算机' and grade < 95);
13.查询同时参加计算机和英语考试的学生的信息
select * from student where id = any(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');
14.将计算机考试成绩按从高到低进行排序
SELECT stu_id, grade FROM score WHERE c_name= '计算机' ORDER BY grade DESC;
15.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 UNION SELECT stu_id FROM score;
16.查询姓张或者姓王的同学的姓名、院系和考试科目及成绩
mysql> SELECT student.id, name,sex,birth,department, address, c_name,grade
-> FROM student, score
-> WHERE
-> (name LIKE '张%' OR name LIKE '王%')
-> and student.id=score.stu_id ;
17.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 student.id, name,sex,birth,department, address, c_name,grade FROM student, score WHERE address LIKE '湖南%' AND student.id=score.stu_id;
