[SQL] [LeetCode] Challenge log 184

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184. Department Highest Salary

Review usage of in, exists

The Employee table holds all employees. Every employee has an Id, a salary, and there is also a column for the department Id.

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+----+-------+--------+--------------+
| Id | Name  | Salary | DepartmentId |
+----+-------+--------+--------------+
| 1  | Joe   | 70000  | 1            |
| 2  | Henry | 80000  | 2            |
| 3  | Sam   | 60000  | 2            |
| 4  | Max   | 90000  | 1            |
+----+-------+--------+--------------+

The Department table holds all departments of the company.

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+----+----------+
| Id | Name     |
+----+----------+
| 1  | IT       |
| 2  | Sales    |
+----+----------+

Write a SQL query to find employees who have the highest salary in each of the departments. For the above tables, Max has the highest salary in the IT department and Henry has the highest salary in the Sales department.

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+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
| IT         | Max      | 90000  |
| Sales      | Henry    | 80000  |
+------------+----------+--------+
Soulution:
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-- exists
select D.name as Department, E.name as Employee, E.salary as Salary
from Employee E join Department D on E.DepartmentId = D.id
where not exists
(
    select *
    from Employee B
    where B.salary > E.salary and B.DepartmentId = E.DepartmentId
)
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-- in
select D.name as Department, E.name as Employee, E.salary as Salary
from Employee E join Department D on E.DepartmentId = D.id
where (E.DepartmentId, E.salary) in
(
    select E.DepartmentId, max(salary)
	from Employee E
	group by E.DepartmentId
)
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