SQL Taskbook Level 2.3
Given a table:
| id | first_name | last_name | salary | department | manager_id | start_work_date |
| 1 | Aaron | Gold | 4300.00 | PHP | 1 | 2012-02-10 |
| 2 | Marina | Page | 4000.00 | React | NULL | 2010-12-10 |
| 3 | Max | Tyler | 1500.00 | PHP | 1 | 2020-05-30 |
| 4 | Oliver | Barrera | 1500.00 | Node.js | NULL | 2020-08-31 |
| 5 | Andrew | Green | 900.00 | PHP | 1 | 2023-08-31 |
Solve the following tasks for it:
List the unique departments in which employees work.
Find employees who are paid above the average salary in their department.
Display the first and last names of employees who have worked for more than 5 years.
Find employees who do not have a manager set (NULL in the manager_id field).
Display a list of employees sorted by hire date in descending order.
