WITH MATERIALIZED expensive_calc AS (
  -- This CTE will be computed once and stored
  SELECT
    emp_id,
    SUM(hours) AS total_hours,
    COUNT(DISTINCT project_id) AS project_count
  FROM project_assignments
  GROUP BY emp_id
)
SELECT
  e.first_name,
  e.last_name,
  ec.total_hours,
  ec.project_count,
  ROUND(e.salary / NULLIF(ec.total_hours, 0), 2) AS hourly_cost
FROM employees e
JOIN expensive_calc ec ON e.emp_id = ec.emp_id
ORDER BY hourly_cost DESC;