数据库后续

-- 添加作者字段
alter table t_hero add author varchar(100);

-- 更新数据

update t_hero set author = "曹雪芹" where id = 1;
update t_hero set author = "曹雪芹" where id = 2;
update t_hero set author = "曹雪芹" where id = 3;
update t_hero set author = "曹雪芹" where id = 4;

update t_hero set author = "吴承恩" where id = 5;
update t_hero set author = "吴承恩" where id = 6;
update t_hero set author = "吴承恩" where id = 7;
update t_hero set author = "吴承恩" where id = 8;

update t_hero set author = "罗贯中" where id = 9;
update t_hero set author = "罗贯中" where id = 10;
update t_hero set author = "罗贯中" where id = 11;
update t_hero set author = "罗贯中" where id = 12;
update t_hero set author = "罗贯中" where id = 13;

update t_hero set author = "施耐庵" where id = 14;
update t_hero set author = "施耐庵" where id = 15;
update t_hero set author = "施耐庵" where id = 16;
update t_hero set author = "施耐庵" where id = 17;
update t_hero set author = "施耐庵" where id = 18;

-- 查看t_hero表
select * from t_hero;

-- 根据id删除数据

delete from t_hero where id = 18;

select * from t_hero;

-- 增加数据
insert into t_hero(name, book, author) VALUES ('武松', '水浒传', '施耐庵');
select * from t_hero;

单表查询

素材：表名：worker-- 表中字段均为中文，比如部门号工资职工号参加工作等

CREATE TABLE `worker` (
`部门号` int(11) NOT NULL,
`职工号` int(11) NOT NULL,
`工作时间` date NOT NULL,
`工资` float(8,2) NOT NULL,
`政治面貌` varchar(10) NOT NULL DEFAULT '群众',
`姓名` varchar(20) NOT NULL,
`出生日期` date NOT NULL,
PRIMARY KEY (`职工号`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC;

INSERT INTO `worker` (`部门号`, `职工号`, `工作时间`, `工资`, `政治面貌`, `姓名`, `出生日期`) VALUES (101, 1001, '2015-5-4', 3500.00, '群众', '张三', '1990-7-1');
INSERT INTO `worker` (`部门号`, `职工号`, `工作时间`, `工资`, `政治面貌`, `姓名`, `出生日期`) VALUES (101, 1002, '2017-2-6', 3200.00, '团员', '李四', '1997-2-8');
INSERT INTO `worker` (`部门号`, `职工号`, `工作时间`, `工资`, `政治面貌`, `姓名`, `出生日期`) VALUES (102, 1003, '2011-1-4', 8500.00, '党员', '王亮', '1983-6-8');
INSERT INTO `worker` (`部门号`, `职工号`, `工作时间`, `工资`, `政治面貌`, `姓名`, `出生日期`) VALUES (102, 1004, '2016-10-10', 5500.00, '群众', '赵六', '1994-9-5');
INSERT INTO `worker` (`部门号`, `职工号`, `工作时间`, `工资`, `政治面貌`, `姓名`, `出生日期`) VALUES (102, 1005, '2014-4-1', 4800.00, '党员', '钱七', '1992-12-30');
INSERT INTO `worker` (`部门号`, `职工号`, `工作时间`, `工资`, `政治面貌`, `姓名`, `出生日期`) VALUES (102, 1006, '2017-5-5', 4500.00, '党员', '孙八', '1996-9-2');

1、显示所有职工的基本信息。

select * from worker;

2、查询所有职工所属部门的部门号，不显示重复的部门号。

select DISTINCT `部门号` from worker;

3、求出所有职工的人数。

select count(*) from worker;

4、列出最高工和最低工资。

select max(`工资`) from worker;
select min(`工资`) from worker;

5、列出职工的平均工资和总工资。

select avg(`工资`) from worker;
select sum(`工资`) from worker;

6、创建一个只有职工号、姓名和参加工作的新表，名为工作日期表。

CREATE TABLE `工作日期表` (
`职工号` int(11) NOT NULL,
`姓名` varchar(20) NOT NULL,
`出生日期` date NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC;

7、显示所有党员的名字。

select `姓名` from worker where `政治面貌` = '党员';

8、列出所有姓刘的职工的职工号、姓名和出生日期。

select `职工号`, `姓名`, `出生日期` from worker where `姓名` like '刘%';

9、列出1960年以前出生的职工的姓名、参加工作日期。

select `姓名`, `工作时间` from worker where `出生日期` < 1960-00-00;

10、列出工资在1000－2000之间的所有职工姓名。

select `姓名` from worker where "工资" > 2000 and "工资" < 3000;

11、列出所有陈姓和李姓的职工姓名。

select `姓名` from worker where `姓名` like '陈%' or `姓名` like '李%';

12、列出所有部门号为2和3的职工号、姓名、党员否。

select `职工号`, `姓名`, `政治面貌` from worker where `部门号` = 102 or `部门号` = 103;

13、将职工表worker中的职工按出生的先后顺序排序。

select * from worker order by "出生日期";

14、显示工资最高的前3名职工的职工号和姓名。

select `职工号`, `姓名` from worker order by `工资` desc limit 3;

15、求出各部门党员的人数。

select count(*) as 党员人数 from worker where 政治面貌="党员";

16、统计各部门的工资和平均工资

select `工资`, (select avg(`工资`) from worker where `部门号` = 101) as 平均工资 from worker where `部门号` = 101;
select `工资`, (select avg(`工资`) from worker where `部门号` = 102) as 平均工资 from worker where `部门号` = 102;

17、列出总人数大于4的部门号和总人数。

select `部门号`, count(*) as 总人数 from worker group by `部门号` having 总人数 > 4;

多表查询

1.创建student和score表

-- 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)
);

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 where id = 902 or id = 904;

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 (2025 - birth) between 2007 and 2003;

8.从student表中查询每个院系有多少人

select department, count(*) as 人数 from student group by department;

9.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;

10.查询李四的考试科目（c_name）和考试成绩（grade）

select name, c_name, grade from score,student where stu_id = 904 and student.id = stu_id;

11.用连接的方式查询所有学生的信息和考试信息

select * from student, score where student.id = stu_id;

12.计算每个学生的总成绩

SELECT
student.id AS 学生ID,
student.name AS 姓名,
SUM(score.grade) AS 总成绩
FROM
student
INNER JOIN
score ON student.id = score.stu_id
GROUP BY
student.id, student.name;

13.计算每个考试科目的平均成绩

select c_name, avg(grade) from score group by c_name;

14.查询计算机成绩低于95的学生信息

select * from student,score where student.id = stu_id and grade < 95 and c_name = "计算机";

15.查询同时参加计算机和英语考试的学生的信息

select * from student,score
where student.id = stu_id
and
student.id in (select stu_id from score where c_name = "计算机")
and
student.id in (select stu_id from score where c_name = "英语")
;

16.将计算机考试成绩按从高到低进行排序

select c_name,grade from score where c_name="计算机" order by 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 id AS 学号 FROM student
UNION
SELECT stu_id AS 学号 FROM score;

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
s.name AS 姓名,
s.department AS 院系,
sc.c_name AS 考试科目,
sc.grade AS 成绩
FROM
student s
JOIN
score sc ON s.id = sc.stu_id
WHERE
s.name LIKE '张%' OR s.name LIKE '王%';