文章目录
- 导出数据
- 1、设置MySQL存放数据的安全目录:
- 2、使用命令查看参数设置是否生效:
- 3、选择要导出表的所有数据库,导出数据为csv格式
- 4、查看导出结果email.csv:
- 5、查看是否与数据库中email表数据一致:
- 导入数据:
- 1、清除email表中数据
- 2、复制导入的CSV格式文件到指定目录
- 3、导入CSV文件:
- 4、查看导入数据的结果:
- 项目七: 各部门工资最高的员工(难度:中等)
- 项目八: 换座位(难度:中等)
- 项目九: 分数排名(难度:中等)
- 项目十:行程和用户(难度:困难)
- 项目十一:各部门前3高工资的员工(难度:中等)
- 项目十二 分数排名 - (难度:中等)
导出数据
将之前创建的任意一张MySQL表导出,且是CSV格式,再将CSV表导入数据库
1、设置MySQL存放数据的安全目录:
windows系统中在my.ini配置secure_file_priv参数
关于secure_file_priv参数说明:
secure-file-priv参数是用来限制LOAD DATA, SELECT … OUTFILE, and LOAD_FILE()传到哪个指定目录的.
- 当secure_file_priv的值为null ,表示限制mysqld 不允许导入|导出;
- 当secure_file_priv的值为/tmp/ ,表示限制mysqld 的导入|导出只能发生在/tmp/目录下;
- 当secure_file_priv的值没有具体值时,表示不对mysqld 的导入|导出做限制;
注意:修改完毕my.ini配置文件后,需要重启mysql才会生效。
2、使用命令查看参数设置是否生效:
mysql> show variables like "secure_file_priv";
+------------------+---------------------------------------------+
| Variable_name | Value |
+------------------+---------------------------------------------+
| secure_file_priv | D:\Program Files\MySQL\mysql-8.0.13-winx64\ |
+------------------+---------------------------------------------+
1 row in set, 1 warning (0.05 sec)
3、选择要导出表的所有数据库,导出数据为csv格式
mysql> use program;
Database changed
mysql> show tables;
+-------------------+
| Tables_in_program |
+-------------------+
| address |
| course |
| email |
| person |
| salary |
| world |
+-------------------+
6 rows in set (0.05 sec)
mysql> select * into outfile 'D:/Program Files/MySQL/mysql-8.0.13-winx64/email.csv'
-> FIELDS TERMINATED BY ','
-> OPTIONALLY ENCLOSED BY '"'
-> LINES TERMINATED BY '\n'
-> from email;
Query OK, 2 rows affected (0.08 sec)
SELECT … INTO 语法可以将查询结果保存到变量或文件中:
SELECT … INTO var_list # 将字段的值保存到变量中
SELECT … INTO OUTFILE # 将选中的行保存到文件中。可以指定列和行的结束符,以生成指定格式的文件。
SELECT … INTO DUMPFILE # 将一个单独的行写入文件中,没有格式
常用参数说明:
- FIELDS TERMINATED BY ‘,’:指定字段分隔符
- OPTIONALLY ENCLOSED BY ‘"’:认为双引号中的是一个独立的字段。Excel 转 CSV 时,有特殊字符(逗号、顿号等)的字段,会自动用双引号引起来
- LINES TERMINATED BY ‘\n’:指定行分隔符,注意,在 Windows 平台上创建的文件,分隔符是 ‘\r\n’
4、查看导出结果email.csv:
使用excel打开:
使用Notepad++打开:
5、查看是否与数据库中email表数据一致:
mysql> select * from email;
+----+---------+
| ID | Email |
+----+---------+
| 1 | a@b.com |
| 2 | c@d.com |
+----+---------+
2 rows in set (0.00 sec)
导入数据:
1、清除email表中数据
两种方式:delete
和truncate
truncate
相当于使用表的结构重新创建表,所有的状态都相当于新表。
不带 where
参数的 delete
则是将表中所有记录一条一条删除。
注意:truncate 比 delete 快,但 truncate 删除后不记录日志,数据无法恢复。
mysql> select * from email;
+----+---------+
| ID | Email |
+----+---------+
| 1 | a@b.com |
| 2 | c@d.com |
+----+---------+
2 rows in set (0.00 sec)
mysql> truncate table email;
Query OK, 0 rows affected (1.25 sec)
mysql> select * from email;
Empty set (0.01 sec)
2、复制导入的CSV格式文件到指定目录
先将要导入的email.csv
复制到D:\Program Files\MySQL\mysql-8.0.13-winx64\data\program
目录下(program
是数据库名称):
3、导入CSV文件:
mysql> LOAD DATA INFILE 'email.csv' INTO TABLE program.email FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' LINES TERMINATED BY '\n';
Query OK, 2 rows affected (0.22 sec)
Records: 2 Deleted: 0 Skipped: 0 Warnings: 0
参数说明跟导出数据的说明一样。
4、查看导入数据的结果:
mysql> select * from email;
+----+---------+
| ID | Email |
+----+---------+
| 1 | a@b.com |
| 2 | c@d.com |
+----+---------+
2 rows in set (0.00 sec)
项目七: 各部门工资最高的员工(难度:中等)
//创建Employee 表,包含所有员工信息,每个员工有其对应的 Id, salary 和 department Id。
mysql> create table Employee(
-> Id int auto_increment primary key,
-> Name varchar(20) not null,
-> Salary int not null,
-> DepartmentId int not null
-> );
Query OK, 0 rows affected (0.87 sec)
//创建Department 表,包含公司所有部门的信息。
mysql> create table Department(
-> Id int auto_increment primary key,
-> Name varchar(20) not null
-> );
Query OK, 0 rows affected (0.88 sec)
mysql> insert into Employee(Name,Salary,DepartmentId)
-> values('Joe',70000,1),
-> ('Henry',80000,2),
-> ('Sam',60000,2),
-> ('Max',90000,1);
Query OK, 4 rows affected (0.19 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> insert into Department
-> values(1,'IT'),
-> (2,'Sales');
Query OK, 2 rows affected (0.21 sec)
Records: 2 Duplicates: 0 Warnings: 0
//编写一个 SQL 查询,找出每个部门工资最高的员工。例如,根据上述给定的表格,Max 在 IT 部门有最高工资,Henry 在 Sales 部门有最高工资。
mysql> select d.Name as Department,e.Name as Employee,e.Salary
-> from Department d,Employee e
-> where e.DepartmentId=d.Id
-> and e.Salary=(Select max(Salary) from Employee where DepartmentId=d.Id);
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| Sales | Henry | 80000 |
| IT | Max | 90000 |
+------------+----------+--------+
2 rows in set (0.00 sec)
项目八: 换座位(难度:中等)
小美是一所中学的信息科技老师,她有一张 seat 座位表,平时用来储存学生名字和与他们相对应的座位 id。
其中纵列的 id 是连续递增的
小美想改变相邻俩学生的座位。
你能不能帮她写一个 SQL query 来输出小美想要的结果呢?
注意:
如果学生人数是奇数,则不需要改变最后一个同学的座位。
//创建seat表,储存student和对应的座位id
mysql> create table seat(
-> id int auto_increment primary key,
-> student varchar(20) not null
-> );
Query OK, 0 rows affected (0.92 sec)
mysql> insert into seat
-> values(1,'Abbot'),
-> (2,'Doris'),
-> (3,'Emerson'),
-> (4,'Green'),
-> (5,'Jeames');
Query OK, 5 rows affected (0.18 sec)
Records: 5 Duplicates: 0 Warnings: 0
mysql> select * from seat;
+----+---------+
| id | student |
+----+---------+
| 1 | Abbot |
| 2 | Doris |
| 3 | Emerson |
| 4 | Green |
| 5 | Jeames |
+----+---------+
5 rows in set (0.00 sec)
//思路:利用id的奇偶性交换相邻学生的id,然后再对id重新排序
mysql> select
-> case when id%2=0 then id-1
-> when id < (select max(id) from seat) then id+1
-> else id
-> end as id,student from seat order by id;
+----+---------+
| id | student |
+----+---------+
| 1 | Doris |
| 2 | Abbot |
| 3 | Green |
| 4 | Emerson |
| 5 | Jeames |
+----+---------+
5 rows in set (0.01 sec)
项目九: 分数排名(难度:中等)
mysql> create table score(
-> Id int auto_increment primary key not null,
-> Score float(5,2) not null);
Query OK, 0 rows affected (1.20 sec)
mysql> insert into score(Score)
-> values(3.50),
-> (3.65),
-> (4.00),
-> (3.85),
-> (4.00),
-> (3.65);
Query OK, 6 rows affected (0.45 sec)
Records: 6 Duplicates: 0 Warnings: 0
mysql> select * from score;
+----+-------+
| Id | Score |
+----+-------+
| 1 | 3.50 |
| 2 | 3.65 |
| 3 | 4.00 |
| 4 | 3.85 |
| 5 | 4.00 |
| 6 | 3.65 |
+----+-------+
6 rows in set (0.00 sec)
//编写一个 SQL 查询来实现分数排名。如果两个分数相同,则两个分数排名(Rank)相同。请注意,平分后的下一个名次应该是下一个连续的整数值。换句话说,名次之间不应该有“间隔”。
//思路:对于每一个分数,从表中找出有多少个大于或等于该分数的不重复分数,然后降序排列
mysql> select Score,
-> (select count(distinct Score) from score as s2 where s2.Score >= s1.Score)`Rank` --注意加``,否则会报错误1064
-> from score as s1
-> order by Score DESC;
+-------+------+
| Score | Rank |
+-------+------+
| 4.00 | 1 |
| 4.00 | 1 |
| 3.85 | 2 |
| 3.65 | 3 |
| 3.65 | 3 |
| 3.50 | 4 |
+-------+------+
6 rows in set (0.00 sec)
项目十:行程和用户(难度:困难)
Trips 表中存所有出租车的行程信息。每段行程有唯一键 Id,Client_Id 和 Driver_Id 是 Users 表中 Users_Id 的外键。Status 是枚举类型,枚举成员为 (‘completed’, ‘cancelled_by_driver’, ‘cancelled_by_client’)。
+----+-----------+-----------+---------+--------------------+----------+
| Id | Client_Id | Driver_Id | City_Id | Status |Request_at|
+----+-----------+-----------+---------+--------------------+----------+
| 1 | 1 | 10 | 1 | completed |2013-10-01|
| 2 | 2 | 11 | 1 | cancelled_by_driver|2013-10-01|
| 3 | 3 | 12 | 6 | completed |2013-10-01|
| 4 | 4 | 13 | 6 | cancelled_by_client|2013-10-01|
| 5 | 1 | 10 | 1 | completed |2013-10-02|
| 6 | 2 | 11 | 6 | completed |2013-10-02|
| 7 | 3 | 12 | 6 | completed |2013-10-02|
| 8 | 2 | 12 | 12 | completed |2013-10-03|
| 9 | 3 | 10 | 12 | completed |2013-10-03|
| 10 | 4 | 13 | 12 | cancelled_by_driver|2013-10-03|
+----+-----------+-----------+---------+--------------------+----------+
Users 表存所有用户。每个用户有唯一键 Users_Id。Banned 表示这个用户是否被禁止,Role 则是一个表示(‘client’, ‘driver’, ‘partner’)的枚举类型。
+----------+--------+--------+
| Users_Id | Banned | Role |
+----------+--------+--------+
| 1 | No | client |
| 2 | Yes | client |
| 3 | No | client |
| 4 | No | client |
| 10 | No | driver |
| 11 | No | driver |
| 12 | No | driver |
| 13 | No | driver |
+----------+--------+--------+
写一段 SQL 语句查出 2013年10月1日 至 2013年10月3日 期间非禁止用户的取消率。基于上表,你的 SQL 语句应返回如下结果,取消率(Cancellation Rate)保留两位小数。
+------------+-------------------+
| Day | Cancellation Rate |
+------------+-------------------+
| 2013-10-01 | 0.33 |
| 2013-10-02 | 0.00 |
| 2013-10-03 | 0.50 |
+------------+-------------------+
方法:
//Users 表存所有用户。每个用户有唯一键 Users_Id。Banned 表示这个用户是否被禁止,Role 则是一个表示(‘client’, ‘driver’, ‘partner’)的枚举类型。
CREATE TABLE Users(
Users_Id INT UNIQUE,
Banned VARCHAR(10),
Role ENUM('client', 'driver', 'partner')
);
INSERT INTO Users
VALUES(1,'No','client'),
(2,'Yes','client'),
(3,'No','client'),
(4,'No','client'),
(10,'No','driver'),
(11,'No','driver'),
(12,'No','driver'),
(13,'No','driver');
SELECT * FROM Users;
//Trips 表中存所有出租车的行程信息。每段行程有唯一键 Id,Client_Id 和 Driver_Id 是 Users 表中 Users_Id 的外键。Status 是枚举类型,枚举成员为 (‘completed’, ‘cancelled_by_driver’, ‘cancelled_by_client’)。
CREATE TABLE Trips(
Id INT AUTO_INCREMENT UNIQUE,
Client_Id INT,
Driver_Id INT,
City_Id INT,
`Status` ENUM('completed', 'cancelled_by_driver', 'cancelled_by_client'),
Request_at DATE,
FOREIGN KEY(Client_Id) REFERENCES Users(Users_Id),
FOREIGN KEY(Driver_Id) REFERENCES Users(Users_Id)
);
INSERT INTO Trips(Client_Id,Driver_Id,City_Id,`Status`,Request_at)
VALUES(1,10,1,'completed','2013-10-01'),
(2,11,1,'cancelled_by_driver','2013-10-01'),
(3,12,6,'completed','2013-10-01'),
(4,13,6,'cancelled_by_client','2013-10-01'),
(1,10,1,'completed','2013-10-02'),
(2,11,6,'completed','2013-10-02'),
(3,12,6,'completed','2013-10-02'),
(2,12,12,'completed','2013-10-03'),
(3,10,12,'completed','2013-10-03'),
(4,13,12,'cancelled_by_driver','2013-10-03');
SELECT * FROM Trips;
//写一段 SQL 语句查出 2013年10月1日 至 2013年10月3日 期间非禁止用户的取消率,取消率(Cancellation Rate)保留两位小数.
//基本思路:先筛选出非禁止用户的信息记录,再利用聚合函数sum与count计算各个日期对应的取消率。
SELECT Request_at AS DAY,ROUND(SUM(STATUS!='completed')/COUNT(STATUS),2) AS 'Cancellation Rate'
FROM Trips t
WHERE t.Client_Id IN (SELECT Users_Id FROM Users WHERE Banned != 'Yes')
AND t.Driver_Id IN (SELECT Users_Id FROM Users WHERE Banned != 'Yes')
AND Request_at BETWEEN '2013-10-01' AND '2013-10-03'
GROUP BY Request_at;
项目十一:各部门前3高工资的员工(难度:中等)
将项目7中的employee表清空,重新插入以下数据(其实是多插入5,6两行):
+----+-------+--------+--------------+
| Id | Name | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1 | Joe | 70000 | 1 |
| 2 | Henry | 80000 | 2 |
| 3 | Sam | 60000 | 2 |
| 4 | Max | 90000 | 1 |
| 5 | Janet | 69000 | 1 |
| 6 | Randy | 85000 | 1 |
+----+-------+--------+--------------+
编写一个 SQL 查询,找出每个部门工资前三高的员工。例如,根据上述给定的表格,查询结果应返回:
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT | Max | 90000 |
| IT | Randy | 85000 |
| IT | Joe | 70000 |
| Sales | Henry | 80000 |
| Sales | Sam | 60000 |
+------------+----------+--------+
此外,请考虑实现各部门前N高工资的员工功能。
//插入数据
INSERT INTO employee(NAME,Salary,DepartmentId)
VALUES('Janet',69000,1), ('Randy',85000,1);
//编写一个 SQL 查询,找出每个部门工资前三高的员工。
SELECT d.NAME Department, e.NAME Employee, e.Salary Salary
FROM Department d, Employee e
WHERE e.DepartmentId = d.Id
AND
(SELECT COUNT(DISTINCT Salary)
FROM Employee
WHERE DepartmentId = d.Id
AND Salary > e.Salary) < 3
;
//编写一个 SQL 查询,找出每个部门工资前N高的员工。与上述SQL语句类似,修改最后的3为N。
项目十二 分数排名 - (难度:中等)
依然是昨天的分数表,实现排名功能,但是排名是非连续的,如下:
+-------+------+
| Score | Rank |
+-------+------+
| 4.00 | 1 |
| 4.00 | 1 |
| 3.85 | 3 |
| 3.65 | 4 |
| 3.65 | 4 |
| 3.50 | 6 |
+-------+------
SELECT Score,
(SELECT COUNT(Score)
FROM score AS s2
WHERE s2.Score > s1.Score
)+1 AS `Rank`
FROM score AS s1
ORDER BY Score DESC;