案例-多表查询、子查询实例（有答案）

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);

3.查询student表的所有记录

select * from student;

4.查询student表的第2条到4条记录

select * from student limit 1,3;

5.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;

6.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';

7.从student表中查询年龄18~22岁的学生信息

select * from student where birth between 1995 and 1999;

8.从student表中查询每个院系有多少人

select count(*) as num ,department from student GROUP BY department;

9.从score表中查询每个科目的最高分

select max(grade),c_name  from score GROUP BY c_name;

10.查询李四的考试科目（c_name）和考试成绩（grade）

SELECT  sc.c_name , sc.grade, st.name
FROM student as st , score as sc
where st.id = sc.stu_id and st.name = '李四';

11.查询所有学生的信息和考试信息

SELECT  *
FROM student as st , score as sc
where st.id = sc.stu_id;

12.计算每个学生的总成绩

SELECT  st.name, SUM(sc.grade)
FROM student as st , score as sc
where st.id = sc.stu_id 
GROUP BY st.name;

13.计算每个考试科目的平均成绩

SELECT  sc.c_name, avg(sc.grade)
FROM student as st , score as sc
where st.id = sc.stu_id 
GROUP BY sc.c_name;

14.查询计算机成绩低于95的学生信息

SELECT  st.id, st.name, st.sex, st.department, st.address, sc.c_name, sc.grade
FROM student as st , score as sc
where st.id = sc.stu_id and sc.c_name = '计算机' and sc.grade < 95;

15.查询同时参加计算机和英语考试的学生的信息

SELECT  *
FROM student as st , score as sc    
where st.id = sc.stu_id and sc.c_name = '计算机' and st.id in 
(SELECT st.id 
FROM student as st , score as sc    
where st.id = sc.stu_id and sc.c_name = '英语');

16.将计算机考试成绩按从高到低进行排序

SELECT  sc.c_name, sc.grade
FROM student as st , score as sc
where st.id = sc.stu_id and sc.c_name = '计算机' ORDER BY sc.grade desc;

17.从student表和score表中查询出学生的学号，然后合并查询结果

SELECT distinct st.id 
FROM student as st , score as sc
where st.id = sc.stu_id ;

18.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  st.name,  st.department,  sc.c_name, sc.grade
FROM student as st , score as sc    
where st.id = sc.stu_id and st.name like '张%' or st.name like '王%';

19.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  st.name, st.birth, st.department, st.address, sc.c_name, sc.grade
FROM student as st , score as sc    
where st.id = sc.stu_id and st.address like '湖南%';