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12-homework-yanjun/sql_max

+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  |
++------------+----------+--------+
+
+解法1：
+select b.Name as Department,a.Name as Employee, max(Salary) as Salary
+from Employee a , Department b
+where a.DepartmentId = b.Id
+group by Department
+
+解法2：
+select b.Name as Department,a.Name as Employee, max(Salary) as Salary
+from Employee a inner join Department b
+on a.DepartmentId = b.Id
+group by Department
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12-homework-yanjun/sql_top3

+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            |
+| 5  | Janet | 69000  | 1            |
+| 6  | Randy | 85000  | 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  |
++------------+----------+--------+
+
+笨解法：
+(select c.Department,c.Employee,c.Salary
+from
+ (select b.Name as Department,a.Name as Employee, a.Salary
+from Employee a
+left join Department b
+on a.DepartmentId = b.Id)c
+where c.Department='IT' order by c.Salary desc limit 3)
+union all
+(select c.Department,c.Employee,c.Salary
+from
+ (select b.Name as Department,a.Name as Employee, a.Salary
+from Employee a
+left join Department b
+on a.DepartmentId = b.Id)c
+where c.Department='Sales' order by c.Salary desc limit 3);
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