176 第二高的薪水
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 |
+---------------------+
答案:
SELECT IFNULL ((SELECT distinct e.Salary from Employee e order by e.Salary DESC limit 1, 1) , null) as SecondHighestSalary;
思路:
先找出第二个,通过分页,再判断空返回null
177 第N高的薪水
编写一个 SQL 查询,获取 Employee 表中第 n 高的薪水(Salary)。
+----+--------+
| Id | Salary |
+----+--------+
| 1 | 100 |
| 2 | 200 |
| 3 | 300 |
+----+--------+
例如上述 Employee 表,n = 2 时,应返回第二高的薪水 200。如果不存在第 n 高的薪水,那么查询应返回 null。+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| 200 |
+------------------------+
答案:
CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
set N = N-1;
RETURN (
SELECT IFNULL ((SELECT distinct e.Salary from Employee e order by e.Salary DESC limit N, 1) , null
));
END
关键点在于要取第N高的要先将N-1,例如取第2高的实际是写的 limit 1,1
178. 分数排名
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 |
+-------+------+
答案:
select s.Score , count(distinct (s1.Score)) as rank from Scores s, Scores s1 where s.Score <= s1.Score group by s.Id
181 超过经理收入的员工
Employee 表包含所有员工,他们的经理也属于员工。每个员工都有一个 Id,此外还有一列对应员工的经理的 Id。
+----+-------+--------+-----------+
| Id | Name | Salary | ManagerId |
+----+-------+--------+-----------+
| 1 | Joe | 70000 | 3 |
| 2 | Henry | 80000 | 4 |
| 3 | Sam | 60000 | NULL |
| 4 | Max | 90000 | NULL |
+----+-------+--------+-----------+
给定 Employee 表,编写一个 SQL 查询,该查询可以获取收入超过他们经理的员工的姓名。在上面的表格中,Joe 是唯一一个收入超过他的经理的员工。+----------+
| Employee |
+----------+
| Joe |
+----------+
解决方案
select e.Name as Employee from Employee e left join Employee e1 on e.ManagerId = e1.Id where e.Salary > e1.Salary;
183 从不订购的客户
某网站包含两个表,Customers 表和 Orders 表。编写一个 SQL 查询,找出所有从不订购任何东西的客户。
Customers 表:
+----+-------+
| Id | Name |
+----+-------+
| 1 | Joe |
| 2 | Henry |
| 3 | Sam |
| 4 | Max |
+----+-------+
Orders 表:+----+------------+
| Id | CustomerId |
+----+------------+
| 1 | 3 |
| 2 | 1 |
+----+------------+
例如给定上述表格,你的查询应返回:+-----------+
| Customers |
+-----------+
| Henry |
| Max |
+-----------+
答案:
# Write your MySQL query statement below
select c1.Name as Customers from Customers c1 where c1.Id not in( select c.Id from Customers c join Orders o on c.Id = o.CustomerId) ;
# solution 2
#select c.Name as Customers from Customers c left join Orders o on c.Id = o.CustomerId where o.CustomerId is null
184. 部门最高薪水
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 |
+------------+----------+--------+
分析:
首先可以找出各部门的最高工资,如下:
select max(Salary) as Salary,DepartmentId from Employee e group by DepartmentId
注意这里想把员工姓名一起找出来是不行的,group by部门编号,只能实现找出各部门最高工资的功能。即:
select max(Salary) as Salary,DepartmentId, name from Employee e group by DepartmentId
这个写法无法找出正确的name属性。
然后可以通过一个in关键字找出employe的信息,同时join Department表。注意这里两个字段的in查询使用括号扩起来,逗号分隔即可。
select d.Name as Department, e1.Name as Employee,e1.Salary
from Department d,Employee e1
where d.Id = e1.DepartmentId
AND (e1.Salary,e1.DepartmentId) in(
select max(Salary) as Salary,DepartmentId from Employee e group by DepartmentId);
185 部门工资前三高的所有员工(困难)
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。
分析:
需要根据部门id进行分组。
找出最高的可以用max函数,找出前三高的工资使用分页是不行的,因为存在工资重复的情况,此题的困难点在这。
尝试对工资根据部门进行排名,相同的名次一样,名次无间隔,再各自取前三名的。