[LeetCode]Sql系列

题目1

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            |

+----+-------+--------+--------------+

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  |

+------------+----------+--------+

代码

# Write your MySQL query statement below

select Department.Name as Department, Employee.Name as Employee,Salary

from Employee join Department

on Employee.DepartmentId = Department.Id

where (DepartmentId,Salary) in

(

select DepartmentId,Max(Salary) as Salary

from Employee

group by DepartmentId

)

题目2

编写一个 SQL 查询，获取 Employee 表中第二高的薪水（Salary） 。

+----+--------+

| Id | Salary |

+----+--------+

| 1  | 100    |

| 2  | 200    |

| 3  | 300    |

+----+--------+

例如上述 Employee 表，SQL查询应该返回 200 作为第二高的薪水。如果不存在第二高的薪水，那么查询应返回 null。

+---------------------+

| SecondHighestSalary |

+---------------------+

| 200                 |

+---------------------+

代码

# Write your MySQL query statement below

select (

select distinct Salary

from employee

order by Salary desc

limit 1,1

) as SecondHighestSalary

题目3

部门表 Department：

+---------------+---------+

| Column Name   | Type    |

+---------------+---------+

| id            | int     |

| revenue       | int     |

| month         | varchar |

+---------------+---------+

(id, month) 是表的联合主键。

这个表格有关于每个部门每月收入的信息。

月份（month）可以取下列值 ["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"]。

 

编写一个 SQL 查询来重新格式化表，使得新的表中有一个部门 id 列和一些对应 每个月 的收入（revenue）列。

查询结果格式如下面的示例所示：

Department 表：

+------+---------+-------+

| id   | revenue | month |

+------+---------+-------+

| 1    | 8000    | Jan   |

| 2    | 9000    | Jan   |

| 3    | 10000   | Feb   |

| 1    | 7000    | Feb   |

| 1    | 6000    | Mar   |

+------+---------+-------+

查询得到的结果表：

+------+-------------+-------------+-------------+-----+-------------+

| id   | Jan_Revenue | Feb_Revenue | Mar_Revenue | ... | Dec_Revenue |

+------+-------------+-------------+-------------+-----+-------------+

| 1    | 8000        | 7000        | 6000        | ... | null        |

| 2    | 9000        | null        | null        | ... | null        |

| 3    | null        | 10000       | null        | ... | null        |

+------+-------------+-------------+-------------+-----+-------------+

注意，结果表有 13 列 (1个部门 id 列 + 12个月份的收入列)。

代码

# Write your MySQL query statement below

select

    id,

    max(if(month = 'Jan',revenue,null)) as Jan_Revenue,

    max(if(month = 'Feb',revenue,null)) as Feb_Revenue,

    max(if(month = 'Mar',revenue,null)) Mar_Revenue,

    max(if(month = 'Apr',revenue,null)) Apr_Revenue,

    max(if(month = 'May',revenue,null)) May_Revenue,

    max(if(month = 'Jun',revenue,null)) Jun_Revenue,

    max(if(month = 'Jul',revenue,null)) Jul_Revenue,

    max(if(month = 'Aug',revenue,null)) Aug_Revenue,

    max(if(month = 'Sep',revenue,null)) Sep_Revenue,

    max(if(month = 'Oct',revenue,null)) Oct_Revenue,

    max(if(month = 'Nov',revenue,null)) Nov_Revenue,

    max(if(month = 'Dec',revenue,null)) Dec_Revenue

from Department

group by id

题目4

Employee 表包含所有员工信息，每个员工有其对应的工号 Id，姓名 Name，工资 Salary 和部门编号 DepartmentId 。

+----+-------+--------+--------------+

| Id | Name | Salary | DepartmentId |

+----+-------+--------+--------------+

| 1 | Joe | 85000 | 1 |

| 2 | Henry | 80000 | 2 |

| 3 | Sam | 60000 | 2 |

| 4 | Max | 90000 | 1 |

| 5 | Janet | 69000 | 1 |

| 6 | Randy | 85000 | 1 |

| 7 | Will | 70000 | 1 |

+----+-------+--------+--------------+

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，找出每个部门获得前三高工资的所有员工。例如，根据上述给定的表，查询结果应返回：

+------------+----------+--------+

| Department | Employee | Salary |

+------------+----------+--------+

| IT | Max | 90000 |

| IT | Randy | 85000 |

| IT | Joe | 85000 |

| IT | Will | 70000 |

| Sales | Henry | 80000 |

| Sales | Sam | 60000 |

+------------+----------+--------+

解释：

IT 部门中，Max 获得了最高的工资，Randy 和 Joe 都拿到了第二高的工资，Will 的工资排第三。销售部门（Sales）只有两名员工，Henry 的工资最高，Sam 的工资排第二。

题解

# Write your MySQL query statement below

select d.Name as Department, e1.Name as Employee, e1.Salary

from Employee e1 join Department d

on e1.DepartmentId = d.Id

where (

    select count(distinct e2.Salary)

    from Employee e2

    where e2.Salary > e1.Salary

    and e2.DepartmentId = e1.DepartmentId

) < 3

题目5

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”。

+----+-------+

| 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    |

+-------+------+

代码

# Write your MySQL query statement below

select s1.Score,(

    select count(distinct s2.Score)

    from Scores s2

    where s2.Score >= s1.Score)as 'Rank'

from Scores s1

order by s1.Score DESC

巴特西

[LeetCode]Sql系列

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