$1.$ Retrieve the names of employees who have no dependents

$2.$ List the names of managers who have at least one dependent.

$3.$ Retrieve the Social Security numbers of all employees who work on project numbers $1,2,$

or $3$

$4.$ Find the sum of the salaries of all employees, the maximum salary, the minimum salary,

and the average salary.

$5.$ Find the sum of the salaries of all employees of the $$Research$$ department, as well as the

maximum salary, the minimum salary, and the average salary in this department

$6.$ Retrieve the total number of employees in the company and the number of employees in

the $$Research$$ department

$7.$ Count the number of distinct salary values in the database.

$8.$ For each department, retrieve the department number, the number of employees in the

department, and their average salary.

$9.$ For each project, retrieve the project number, the project name, and the number of

employees who work on that project.

$10.$ For each project on which more than two employees work, retrieve the project number, the

project name, and the number of employees who work on the project.

$11.$ For each project, retrieve the project number, the project name, and the number of

employees from department $5$ who work on the project.