Day4 MySQL入门学习

其他 2019-04-09 17:14:05 阅读次数: 0
版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/qq_27283619/article/details/89064559

MySQL实战

1. 数据导入、导出

1.1 数据导出CSV

使用SELECT…INTO OUTIFLE语句导出数据以下示例导出为CSV格式文件。

语法

mysql> SELECT * FROM courses
    -> INTO OUTFILE "D:/DatabaseSoftware/output/courses6.csv"
    -> FIELDS TERMINATED BY ','
    -> OPTIONALLY ENCLOSED BY '"'
    -> LINES TERMINATED BY'\r\n';
Query OK, 10 rows affected (0.00 sec)

参数说明

  • INTO OUTFILE “导出的目录名”
    指定导出的目录和文件名。导出时报错"ERROR 1290 (HY000): The MySQL server is running with the --secure-file-priv option so it cannot execute this statement"和目录名的注意事项可以参考这篇文章。【错误】MySQL5.7导出数据时提示ERROR 1290 (HY000)-secure-file-priv错误
  • FIELDS TERMINATED BY ‘字段分隔符’
    定义字段间的分隔符。
  • OPTIONALLY ENCLOSED BY ‘字段包围符’
    定义包围字段的字符（数值型字段无效）。
  • LINES TERMINATED BY ‘行分隔符’
    定义每行的分隔符。
  • 解决导出csv中文乱码问题：
    将csv用txt打开，另存为，选择utf8编码即可。

1.2 CSV数据导入

MySQL 中提供了LOAD DATA INFILE语句来插入数据。与INTO OUTFILE为逆操作。

语法

mysql> LOAD DATA LOCAL INFILE 'D:/DatabaseSoftware/output/courses9.csv' INTO TABLE courses
    -> FIELDS TERMINATED BY ','
    -> OPTIONALLY ENCLOSED BY '"'
    -> LINES TERMINATED BY '\r\n';
Query OK, 11 rows affected (0.07 sec)
Records: 11 Deleted: 0 Skipped: 0 Warnings: 0
mysql> SELECT * FROM courses;
+---------+-----------+
| student | class |
+---------+-----------+
| "A" | Math |
| B | English |
| C | Math |
| D | Biology |
| E | Math |
| F | Computer |
| G | Math |
| H | Math |
| I | Math |
| A | Math |
| J | 计算机 |
+---------+-----------+
11 rows in set (0.00 sec)

2 作业

2.1 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。

Id Name Salary DepartmentId
1 Joe 70000 1
2 Henry 80000 2
3 Sam 60000 2
4 Max 90000 1

创建Department 表，包含公司所有部门的信息。

Id Name
1 IT
2 Sales

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。

Department Employee Salary
IT Max 90000
Sales Henry 80000
  • Step 1 建表并添加数据
-- 创建Employee表
mysql> CREATE TABLE IF NOT EXISTS Employee(
    -> Id INT NOT NULL,
    -> Name VARCHAR(50),
    -> Salary INT,
    -> DepartmentId INT,
    -> PRIMARY KEY(Id)
    -> );
Query OK, 0 rows affected (0.16 sec)
-- 向表Employee添加数据
mysql> INSERT INTO Employee(Id, Name, Salary, DepartmentId)
    -> VALUES(1, 'Joe', 70000, 1),
    -> (2, 'Henry', 80000, 2),
    -> (3, 'Sam', 60000, 2),
    -> (4, 'Max', 90000, 1);
Query OK, 4 rows affected (0.04 sec)
Records: 4 Duplicates: 0 Warnings: 0
-- 查看Employee表的内容
mysql> SELECT * FROM Employee;
+----+-------+--------+--------------+
| Id | Name | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1 | Joe | 70000 | 1 |
| 2 | Henry | 80000 | 2 |
| 3 | Sam | 60000 | 2 |
| 4 | Max | 90000 | 1 |
+----+-------+--------+--------------+
4 rows in set (0.00 sec)
-- 创建Department表
mysql> CREATE TABLE IF NOT EXISTS Department(
    -> Id INT NOT NULL,
    -> Name VARCHAR(50),
    -> PRIMARY KEY(Id)
    -> );
Query OK, 0 rows affected (0.18 sec)
-- 向Department表中添加数据
mysql> INSERT INTO Department(Id, Name)
    -> VALUES(1, 'IT'),
    -> (2, 'Sales');
Query OK, 2 rows affected (0.04 sec)
Records: 2 Duplicates: 0 Warnings: 0
-- 查看Department表中数据
mysql> SELECT * FROM Department;
+----+-------+
| Id | Name |
+----+-------+
| 1 | IT |
| 2 | Sales |
+----+-------+
2 rows in set (0.00 sec)
  • Step 2 查询语句
mysql> SELECT d.Name AS Department, e.Name AS Employee, e.Salary AS Salary
    -> FROM Employee AS e, Department AS d
    -> WHERE e.DepartmentId=d.Id AND
    -> Salary=(SELECT MAX(Salary) FROM Employee WHERE e.DepartmentId=d.Id);
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| Sales | Henry | 80000 |
| IT | Max | 90000 |
+------------+----------+--------+
2 rows in set (0.00 sec)

2.2 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？
请创建如下所示seat表：
示例：

id student
1 Abbot
2 Doris
3 Emerson
4 Green
5 Jeames

假如数据输入的是上表，则输出结果如下：

id student
1 Doris
2 Abbot
3 Green
4 Emerson
5 Jeames

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。

  • Step 1 创建表并添加数据
-- 创建表seat
mysql> CREATE TABLE IF NOT EXISTS seat(
    -> id INT NOT NULL AUTO_INCREMENT,
    -> student varchar(50),
    -> PRIMARY KEY (id)
    -> );
Query OK, 0 rows affected (0.20 sec)
-- 向表seat添加数据
mysql> INSERT INTO seat(student)
    -> VALUES('Abbot'), ('Doris'), ('Emerson'),('Green'), ('Jeames');
Query OK, 5 rows affected (0.05 sec)
Records: 5 Duplicates: 0 Warnings: 0
-- 查看表内容
mysql> SELECT * FROM seat;
+----+---------+
| id | student |
+----+---------+
| 1 | Abbot |
| 2 | Doris |
| 3 | Emerson |
| 4 | Green |
| 5 | Jeames |
+----+---------+
5 rows in set (0.00 sec)
  • Step 2 查询语句
mysql> SELECT (CASE
    -> WHEN id%2 != 0 AND id !=(SELECT COUNT(*) FROM seat) THEN id+1
    -> WHEN id%2 != 0 AND id =(SELECT COUNT(*) FROM seat) THEN id
    -> ELSE id-1
    -> 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 (0.00 sec)

2.3 项目九: 分数排名（难度：中等）

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”。
创建以下score表：

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Id Score
1 3.50
2 3.65
3 4.00
4 3.85
5 4.00
6 3.65

例如，根据上述给定的 Scores 表，你的查询应该返回（按分数从高到低排列）：

Score Rank
4.00 1
4.00 1
3.85 2
3.65 3
3.65 3
3.50 4
  • Step 1 创建表并添加数据
-- 创建score表
mysql> CREATE TABLE IF NOT EXISTS score(
    -> Id INT,
    -> Score FLOAT(5,2)
    -> );
Query OK, 0 rows affected (0.13 sec)
-- 向score表添加数据
mysql> INSERT INTO score(Id, Score)
    -> VALUES(1, 3.50),(2, 3.65),(3, 4.00),(4, 3.85),(5, 4.00),(6, 3.65);
Query OK, 6 rows affected (0.06 sec)
Records: 6 Duplicates: 0 Warnings: 0
-- 查看score表数据
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)
  • Step 2 查询语句
mysql> SELECT Score, (SELECT COUNT(DISTINCT Score) FROM score AS s2 WHERE s2.Score>=s1.Score) As Rank
    -> 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)

2.4 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
  • Step 1
-- 创建Trips表
mysql> CREATE TABLE IF NOT EXISTS Trips(
    -> Id INT NOT NULL,
    -> Client_Id INT NOT NULL,
    -> Drivre_Id INT NOT NULL,
    -> City_Id INT,
    -> Status ENUM('completed', 'cancelled_by_driver', 'cancelled_by_client') NULL,
    -> Request_at VARCHAR(50) NULL,
    -> PRIMARY KEY (Id)
    -> );
Query OK, 0 rows affected (0.16 sec)
-- 向Tirps表添加数据
mysql> INSERT INTO Trips(Id, Client_Id, Driver_Id, City_Id, Status, Request_at)
    -> VALUES(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');
Query OK, 10 rows affected (0.03 sec)
Records: 10 Duplicates: 0 Warnings: 0
-- 查看Tirps表数据
mysql> SELECT * FROM Trips;
+----+-----------+-----------+---------+---------------------+------------+
| 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 |
+----+-----------+-----------+---------+---------------------+------------+
10 rows in set (0.00 sec)
-- 创建表Users
mysql> CREATE TABLE IF NOT EXISTS Users(
    -> Users_Id INT NOT NULL,
    -> Banned VARCHAR(50),
    -> Role ENUM('client', 'driver', 'partner')
    -> );
Query OK, 0 rows affected (0.17 sec)
-- 向表Users添加数据
mysql> INSERT INTO Users(Users_Id, Banned, Role)
    -> 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');
Query OK, 8 rows affected (0.03 sec)
Records: 8 Duplicates: 0 Warnings: 0
-- 查看表Users中数据
mysql> SELECT * FROM Users;
+----------+--------+--------+
| 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 |
+----------+--------+--------+
8 rows in set (0.00 sec)
  • Step 2 查询语句
mysql> SELECT t.Request_at AS 'Day',
    -> ROUND((SUM(CASE WHEN t.Status='completed' THEN 0 ELSE 1 END))/COUNT(*),2) AS 'Cancellation Rate'
    -> FROM Trips AS t
    -> INNER JOIN Users AS u
    -> ON u.Users_Id = t.Client_Id AND u.Banned='No'
    -> GROUP BY t.Request_at;
+------------+-------------------+
| Day | Cancellation Rate |
+------------+-------------------+
| 2013-10-01 | 0.33 |
| 2013-10-02 | 0.00 |
| 2013-10-03 | 0.50 |
+------------+-------------------+
3 rows in set (0.00 sec)

2.5 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。

  • Step 1 清除表并重新添加数据
-- 清楚employee表
mysql> TRUNCATE TABLE employee;
Query OK, 0 rows affected (0.14 sec)
mysql> SELECT * FROM employee;
Empty set (0.00 sec)
-- 想employee中添加数据
mysql> INSERT INTO employee(Id, Name, Salary, DepartmentId)
    -> VALUES(1, 'Joe', 70000, 1),
    -> (2, 'Henry', 80000, 2),
    -> (3, 'Sam', 60000, 2),
    -> (4, 'Max', 90000, 1),
    -> (5, 'Janet', 69000, 1),
    -> (6, 'Randy', 85000, 1);
Query OK, 6 rows affected (0.03 sec)
Records: 6 Duplicates: 0 Warnings: 0
-- 查看表
mysql> SELECT * FROM employee;
+----+-------+--------+--------------+
| 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 |
+----+-------+--------+--------------+
6 rows in set (0.00 sec)
  • Step 2 查询语句
    思路：
mysql> SELECT d.Name AS Department, e1.Name AS Employee, e1.Salary AS Salary
    -> FROM employee AS e1
    -> JOIN department AS d
    -> ON e1.DepartmentId=d.id
    -> WHERE (SELECT COUNT(DISTINCT e2.Salary)
    -> FROM employee AS e2
    -> WHERE e2.Salary > e1.Salary AND
    -> e1.DepartmentId = e2.DepartmentId) < 3
    -> ORDER BY d.Name, e1.Salary DESC;
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT | Max | 90000 |
| IT | Randy | 85000 |
| IT | Joe | 70000 |
| Sales | Henry | 80000 |
| Sales | Sam | 60000 |
+------------+----------+--------+
5 rows in set (0.00 sec)

2.6 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
  • 查询语句
mysql> SELECT Score, (SELECT COUNT(*) FROM score As s2 WHERE s2.Score > s1.Score)+1 As 'Rank'
    -> FROM score AS s1
    -> ORDER BY Score DESC;
+-------+------+
| Score | Rank |
+-------+------+
| 4.00 | 1 |
| 4.00 | 1 |
| 3.85 | 3 |
| 3.65 | 4 |
| 3.65 | 4 |
| 3.50 | 6 |
+-------+------+
6 rows in set (0.00 sec)

3 参考资料

  1. MySQL 导出数据
  2. csv文件导入Mysql

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