Tables: department, dept_emp, dept_manager, employees, salaries, titles

department (columns): dept_no, dept_name

dept_emp (columns): emp_no, dept_no, from_date, to_date

dept_manager (columns): emp_no, dept_no, from_date, to_date

employees (columns): emp_no, birth_date, first_name, last_name, gender, hire_date

salaries (columns): emp_no, salary, from_date, to_date

titles (columns): emp_no, title, from_date, to_date

I need help with writing SQL queries for the questions below. The information about the tables in the SQL database are listed above.

1) What queries are needed for the following:

a) Retrieve the name (first name and last name) of employees based on their department and sort them base on their Salary descending.

b) Is there any employee who does not have a manager?

c) Is there any department which does not have any employee?