SQL-資料庫刷題

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因是個人總結，只列出對自己有用的或較難的：

leetcode 標記難度 困難需求：-- 部門工資前三高的員工Employee 表包含所有員工資訊，每個員工有其對應的 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            || 5  | Janet | 69000  | 1            || 6  | Randy | 85000  | 1            |+----+-------+--------+--------------+Department 表包含公司所有部門的資訊。+----+----------+| Id | Name     |+----+----------+| 1  | IT       || 2  | Sales    |+----+----------+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  |+------------+----------+--------+第一種解法：;with Employee(Id,Name,Salary,DepartmentId) AS(  select 1,'Joe','70000',1 union allselect 2,'Henry','80000',2 union allselect 3,'Sam','60000',2 union allselect 4,'Max','90000',1 union allselect 5,'Janet','69000',1 union allselect 6,'Randy','85000',1), Department(Id,Name) AS( SELECT 1,'IT' UNION ALL SELECT 2,'Sales' ) select d.Name as Department,e.Name as Employee,e.Salary from  ( SELECT *,ROW_NUMBER()OVER(partition by DepartmentId order by Salary desc) as Rank FROM Employee)  e                                             join Department d on e.DepartmentId = d.Id                                             where Rank<=3                                             order by d.Id ASC第二種解法：為了避免 有相同排名出現，採用 DENSE_RANK  密級排名 select d.Name as Department,e.Name as Employee,e.Salary from  ( SELECT *,Dense_Rank()OVER(partition by DepartmentId order by Salary desc) as Rank FROM Employee)  e                                             join Department d on e.DepartmentId = d.Id                                             where Rank<=3                                             order by d.Id ASC

leetcode 難度標記： 簡單給定一個 Weather 表，編寫一個 SQL 查詢，來尋找與之前（昨天的）日期相比溫度更高的所有日期的 Id。+---------+------------------+------------------+| Id(INT) | RecordDate(DATE) | Temperature(INT) |+---------+------------------+------------------+|       1 |       2015-01-01 |               10 ||       2 |       2015-01-02 |               25 ||       3 |       2015-01-03 |               20 ||       4 |       2015-01-04 |               30 |+---------+------------------+------------------+例如，根據上述給定的 Weather 表格，返回如下 Id:+----+| Id |+----+|  2 ||  4 |+----+select Id from Weather w where Temperature > (select Temperature from Weather l  where dateadd(day,1,l.RecordDate) = w.RecordDate)

leetcode 難度標記： 簡單編寫一個 SQL 查詢，擷取 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查詢應該返回 200 作為第二高的薪水。如果不存在第二高的薪水，那麼查詢應返回 null。+---------------------+| SecondHighestSalary |+---------------------+| 200                 |+---------------------+解法：SELECT MAX(SALARY) AS SecondHighestSalary FROM Employee WHERE Salary <(SELECT MAX(SALARY) FROM Employee)

leetcode 難度標記： 中等Employee 表包含所有員工資訊，每個員工有其對應的 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 表包含公司所有部門的資訊。+----+----------+| 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。+------------+----------+--------+| Department | Employee | Salary |+------------+----------+--------+| IT         | Max      | 90000  || Sales      | Henry    | 80000  |+------------+----------+--------+/* Write your T-SQL query statement below */select d.Name as Department      ,e.Name as Employee      ,e.Salary as Salaryfrom Employee e       join Department d on e.DepartmentId = d.Id      join(  SELECT DepartmentId                    ,max(Salary) as Salary                     FROM Employee  Group by DepartmentId            )              grp on e.Salary = grp.Salary              and e.DepartmentId = grp.DepartmentId

SQL-資料庫刷題