GEP's people analytics team needs a quick salary-extremes report for its workforce data. Write a PostgreSQL query to identify every employee whose non-null salary is either the highest or lowest in the employees table, without using subqueries or CTEs.
salary_type label.Highest or Lowest.NULL, and order the result from highest salary to lowest salary.| Column | Type | Description |
|---|---|---|
| employee_idPK | INTEGER | Unique employee identifier |
| employee_name | VARCHAR(100) | Employee's full name |
| department | VARCHAR(80) | GEP department |
| salary | NUMERIC(12,2) | Annual employee salary |