/* ------------------------------------------------------------------------ */
/* Write and test the following queries ----------------------------------- */
/* ------------------------------------------------------------------------ */

/* You can use aggregate functions, e.g. MIN, SUM, COUNT. */
/* You might want to add records in the tables for testing correctness of your answers. Feel free to modify 'emp.sql'. */


/* 1. How many employees are there? */

/* 2. Find the average salary of employees who work in Dallas. */

/* 3. How many employees work on at least one project? */

/* 4. Which departments have at least two employees such that each of them is assigned to at least two projects? */

/* 5. What is the total yearly payroll (sum of 12 * monthly salaries)? */

/* 6. What is the average yearly payroll per department, including those with no employees? */

/* 7. Using regular expressions, list all projects with name containing the letter V (upper or lower case).
Docs: https://www.postgresql.org/docs/current/functions-matching.html */

/* 8. List all projects with name starting with N, each of them with all employees assigned to it. */

/* 9. Which departments have at least one employee for each of the projects? */

/* 10. How many employees participate in all of the projects? */

/* 11. Find all departments such that each of their employees is assigned to a project. */

/* 12. Find tuples [D, J, Sum, Average] which, for each pair [D, J], state the sum of salaries and average salary of employees who work in department D and do job J. */

/* 13. Find the jobs with the maximal standard deviation of salaries. */

/* 14. For each employee, count the number of projects he works on. */

/* 15. Find employees working on all projects except exactly one. */

/* 16. How many times more does the president earn than the lowest-paid employee? */

/* 17. Find tuples [Y, N], where N is number of employees hired in the year Y (the resuslt contains only years when an employee was hired) */

/* 18. For each year since 1990, find number of employees hired in that year (the resuslt must contain also years when no employee was hired). Hint: use PostgreSQL function generate_series(). */