多表联合查询

1.创建student表

mysql> 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)
    -> );

 2.创建score表

mysql> 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)
    -> );

 3.为student表和score表增加记录

student

mysql> INSERT INTO student VALUES( 901,'张老大', '男',1985,'计算机系', '北京市海淀区');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO student VALUES( 902,'张老二', '男',1986,'中文系', '北京市昌平区');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO student VALUES( 903,'张三', '女',1990,'中文系', '湖南省永州市');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO student VALUES( 904,'李四', '男',1990,'英语系', '辽宁省阜新市');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO student VALUES( 905,'王五', '女',1991,'英语系', '福建省厦门市');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO student VALUES( 906,'王六', '男',1988,'计算机系', '湖南省衡阳市');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO student VALUES( 907,'彭智卓', '男',2003,'中文.系', '北京市海淀区');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO student VALUES( 908,'梁浩东', '男',2005,'中文系', '北京市海淀区');
Query OK, 1 row affected (0.00 sec)

 score

mysql> INSERT INTO score VALUES(NULL,901, '计算机',98);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO score VALUES(NULL,901, '英语', 80);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO score VALUES(NULL,902, '计算机',65);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO score VALUES(NULL,902, '中文',88);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO score VALUES(NULL,903, '中文',95);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO score VALUES(NULL,904, '计算机',70);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO score VALUES(NULL,904, '英语',92);
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO score VALUES(NULL,905, '英语',94);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO score VALUES(NULL,906, '计算机',90);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO score VALUES(NULL,906, '英语',85);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO score VALUES(NULL,907, '中文',85);
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO score VALUES(NULL,908, '中文',85);
Query OK, 1 row affected (0.01 sec)

 4.查表

1.查询student表的所有记录

mysql> select *from student;

 2.查询student表的第2条到4条记录

mysql> select *from student limit 1,3;     //返回第2、3和4条记录。在LIMIT子句中，第一个参数指定要跳过的记录数量（起始索引为0），第二个参数指定要返回的记录数量。

 3.从student表查询所有学生的学号（id）、姓名（name）和院系（department）的信息

mysql> 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

mysql> select *from student where department in ('计算机系','英语系');

5.从student表中查询年龄18~22岁的学生信息

mysql> select *from student where year(current_date()) - birth >= 18 and year(current_date()) - birth <= 22;

6.从student表中查询每个院系有多少人    

 mysql>select department, count(*) as total_students
    -> from student
    -> group by department;       

 7.从score表中查询每个科目的最高分

   mysql> select c_name, max(grade) as 最高成绩 from score group by c_name;

8.查询李四的考试科目（c_name）和考试成绩（grade）

mysql> 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

mysql> select student.id, student.name, student.birth, score.c_name, score.grade from studennt join score on student.id = score.stu_id;

10.计算每个学生的总成绩

mysql> select student.id, student.name, sum(score.grade) as total_grade
    -> from student
    -> join score on student.id = score.stu_id
    -> group by  student.id, student.name;

11.计算每个考试科目的平均成绩

 mysql> select score.c_name, avg(score.grade) as average_grade
    -> from score
    -> group by score.c_name;

12.查询计算机成绩低于95的学生信息

 mysql> SELECT student.id, student.name, student.birth, score.grade
    -> from student
    -> join score on student.id = score.stu_id
    -> where score.c_name = '计算机' and score.grade < 95;

13.查询同时参加计算机和英语考试的学生的信息

mysql>select t1.id, t1.name, t1.sex, t1.birth, t1.department, t1.address from (select stu.*, score.c_name from student as stu inner join score on stu.id=score.stu_id where score.c_name='计算机')as t1 inner join  (select stu.*, score.c_name from student as stu inner join score on stu.id=score.stu_id where score.c_name='英语') as t2 on t1.id = t2.id;

 

14.将计算机考试成绩按从高到低进行排序

mysql> SELECT student.id, student.name, student.birth, score.grade
    -> FROM student
    -> JOIN score ON student.id = score.stu_id
    -> WHERE score.c_name = '计算机'
    -> ORDER BY score.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

mysql> 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 s.name, s.department, sc.c_name, sc.grade
    -> FROM student s
    -> JOIN score sc ON s.id = sc.stu_id
    -> WHERE s.name LIKE '张%' OR s.name LIKE '王%';

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

mysql> SELECT s.name, TIMESTAMPDIFF(YEAR, s.birth, CURDATE()) AS age, s.department, sc.c_name, sc.grade
    -> FROM student s
    -> JOIN score sc ON s.id = sc.stu_id
    -> WHERE s.address LIKE '湖南%';