Given an employees table (id, name, dept, salary, hire_date, manager_id), write SQL for: (1) All employees in IT dept, (2) Employees hired after 2020 sorted by salary DESC, (3) Top 5 highest paid, (4) Unique departments, (5) Employees with NULL manager (top-level), (6) Names starting with "A", (7) Salary between 50k-100k.
