SELECT * FROM dept_emp;
SELECT * FROM salaries;
SELECT COUNT(*) FROM employees;
SELECT * FROM employees;

SELECT dept_no, AVG(salary) as avg_s FROM dept_emp as d JOIN salaries as s ON d.emp_no = s.emp_no GROUP BY dept_no;

SELECT emp_no, MAX(salary) as max_s FROM salaries GROUP BY emp_no;

SELECT MAX(salary) as max_s FROM salaries;
SELECT * FROM salaries WHERE salary = 155709;
DELETE FROM salaries WHERE emp_no = 47978;

SELECT dept_no, COUNT(DISTINCT emp_no) as count_s FROM dept_emp GROUP BY dept_no;

SELECT emp_no, salary FROM salaries WHERE to_date = "9999-01-01";
SELECT dept_no, SUM(s.salary) FROM dept_emp as d
  JOIN salaries as s
  ON d.emp_no = s.emp_no WHERE s.to_date = "9999-01-01" AND d.to_date = "9999-01-01" GROUP BY dept_no;