Consider an
employee_id (int)
employee_name (varchar)
department (varchar)
joining_date (date)
salary (decimal)
Highest Earner by Department:
Find the employee with the highest salary in each department.
Average Salary by Department and Year:
Calculate the average salary for each department per year.
Longest Serving Employee:
Identify the employee with the longest tenure.
Please provide concise SQL queries for these analyses, emphasizing simplicity and efficiency. Thanks!