mysql 兩個表合並查詢 字段交換
項目七: 各部門工資最高的員工（難度：中等）
創建 Employee 表，包含所有員工信息，每個員工有其對應的 Id, salary 和 department Id。
create table Employee(
Id int auto_increment primary key,
Name varchar not null,
Salary int not null,
DepartmentId int not null
);
insert into Emploee (Name,Salary,DepartmentId) values(Joe,70000,1);
insert into Emploee(Name,Salary,DepartmentId) values(Henry,80000,2);
insert into Emploee(Name,Salary,DepartmentId) values(Sam,60000,2);
insert into Emploee(Name,Salary,DepartmentId) values(Max,90000,1);
+----+-------+--------+--------------+
| Id | Name | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1 | Joe | 70000 | 1 |
| 2 | Henry | 80000 | 2 |
| 3 | Sam | 60000 | 2 |
| 4 | Max | 90000 | 1 |
+----+-------+--------+--------------+
創建 Department 表，包含公司所有部門的信息。
create table Department(
Id int primary key auto_increment,
Name varchar not null
);
insert into Department(Name) values (IT);
insert into Department(Name) values (Sales);
+----+----------+
| Id | Name |
+----+----------+
| 1 | IT |
| 2 | Sales |
+----+----------+
編寫一個 SQL 查詢，找出每個部門工資最高的員工。例如，根據上述給定的表格，Max 在 IT 部門有最高工資，Henry 在 Sales 部門有最高工資。
select Department.Name as Department,Emploe.Name as Emploee,max(Emploee.Salary) as Salary from Emploee,Department where Employee.Id=Department.Id group by Emploee.DepartmentId;
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT | Max | 90000 |
| Sales | Henry | 80000 |
+------------+----------+--------+
項目八: 換座位（難度：中等）
小是一所中學的信息科技老師，她有一張 seat 座位表，平時用來儲存學生名字和與他們相對應的座位 id。
其中縱列的 id 是連續遞增的
小美想改變相鄰倆學生的座位。
你能不能幫她寫一個 SQL query 來輸出小美想要的結果呢？
請創建如下所示 seat 表：
示例：
create table seat(
id int primary key auto_increment,
student varchar not null
);
insert into seat(student) values(Abbot);
insert into seat(student) values(Doris);
insert into seat(student) values(Emerson);
insert into seat(student) values(Green);
insert into seat(student) values(Jeames);
+---------+---------+
| id | student |
+---------+---------+
| 1 | Abbot |
| 2 | Doris |
| 3 | Emerson |
| 4 | Green |
| 5 | Jeames |
+---------+---------+
假如數據輸入的是上表，則輸出結果如下：
UPDATE seat s1
JOIN seat s2
ON (s1.id % 2 = 1 AND s2.id = s1.id+1)
SET s1.student=s2.student,s2.student=s1.student
WHERE s1.id+1 <> null;
+---------+---------+
| id | student |
+---------+---------+
| 1 | Doris |
| 2 | Abbot |
| 3 | Green |
| 4 | Emerson |
| 5 | Jeames |
+---------+---------+
註意：
如果學生人數是奇數，則不需要改變最後一個同學的座位
項目九: 分數排名（難度：中等）
編寫一個 SQL 查詢來實現分數排名。如果兩個分數相同，則兩個分數排名（Rank）相同。請註意，平分後的下一個名次應該是下一個連續的整數值。換句話說，名次之間不應該有“間隔”。
創建以下 score 表：
+----+-------+
| Id | Score |
+----+-------+
| 1 | 3.50 |
| 2 | 3.65 |
| 3 | 4.00 |
| 4 | 3.85 |
| 5 | 4.00 |
| 6 | 3.65 |
+----+-------+
create table score(
Id int auto_increment primary key,
Score float not null
);
例如，根據上述給定的 scores 表，你的查詢應該返回（按分數從高到低排列）：
+-------+------+
| Score | Rank |
+-------+------+
| 4.00 | 1 |
| 4.00 | 1 |
| 3.85 | 2 |
| 3.65 | 3 |
| 3.65 | 3 |
| 3.50 | 4 |
+-------+------+
SELECT Score,
CASE
WHEN @prevRank = Score THEN @curRank
WHEN @prevRank := Score THEN @curRank := @curRank + 1
END AS Rank
FROM scores,
(SELECT @curRank :=0, @prevRank := NULL)
ORDER BY Score desc;
項目十：行程和用戶（難度：困難）
Trips 表中存所有出租車的行程信息。每段行程有唯一鍵 Id，Client_Id 和 Driver_Id 是 Users 表中 Users_Id 的外鍵。Status 是枚舉類型，枚舉成員為 (‘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 表存所有用戶。每個用戶有唯一鍵 Users_Id。Banned 表示這個用戶是否被禁止，Role 則是一個表示（‘client’, ‘driver’, ‘partner’）的枚舉類型。
+----------+--------+--------+
| 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 |
+----------+--------+--------+
寫一段 SQL 語句查出 2013年10月1日 至 2013年10月3日 期間非禁止用戶的取消率。基於上表，你的 SQL 語句應返回如下結果，取消率（Cancellation Rate）保留兩位小數。
+------------+-------------------+
| Day | Cancellation Rate |
+------------+-------------------+
| 2013-10-01 | 0.33 |
| 2013-10-02 | 0.00 |
| 2013-10-03 | 0.50 |
+------------+-------------------+
select t1.Request_at,t1.c1/t2.c2 as Cancellation Rate from
(select count(Status) as c1 Request_at from Trips where Client_Id in (select Users_id from Users where Role=client && Banned=No;) and Status <> completed group by Request_at;) t1,
(select count(Status) as c2 Request_at from Trips where Client_Id in (select Users_id from Users where Role=client && Banned=No;) group by Request_at;) t2
where
t1.Request_at=t2.Request_at;
項目十一：各部門前3高工資的員工（難度：中等）
將項目7中的 employee 表清空，重新插入以下數據（其實是多插入5,6兩行）：
+----+-------+--------+--------------+
| 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 |
+----+-------+--------+--------------+
編寫一個 SQL 查詢，找出每個部門工資前三高的員工。例如，根據上述給定的表格，查詢結果應返回：
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT | Max | 90000 |
| IT | Randy | 85000 |
| IT | Joe | 70000 |
| Sales | Henry | 80000 |
| Sales | Sam | 60000 |
+------------+----------+--------+
此外，請考慮實現各部門前N高工資的員工功能。
select Department.Name as Department,EmployeeName as Employee,Employee.Salary from
Department join Employee on
order by Employee.salary
desc
limit 3
group by
Department.name
where
Employee.Department_Id=Department.Id;
項目十二 分數排名 - （難度：中等）
依然是昨天的分數表，實現排名功能，但是排名是非連續的，如下：
+-------+------+
| Score | Rank |
+-------+------+
| 4.00 | 1 |
| 4.00 | 1 |
| 3.85 | 3 |
| 3.65 | 4 |
| 3.65 | 4 |
| 3.50 | 6 |
+-------+------
SELECT Score Rank FROM
(SELECT Score,
@curRank := IF(@prevRank = Score, @curRank, @incRank) AS Rank,
@incRank := @incRank + 1,
@prevRank := Score
FROM scores,(
SELECT @curRank :=0, @prevRank := NULL, @incRank := 1
)
ORDER BY Score desc;
mysql 兩個表合並查詢 字段交換