Joining subqueries

subq_join.sql

SELECT DISTINCT
    job_history.employee_id, 
    employees.first_name,
    x.max_start,
    y.min_start
FROM hr.job_history
JOIN hr.employees
    ON job_history.employee_id = employees.employee_id
JOIN
    (SELECT employee_id, max(start_date) as max_start
            FROM hr.job_history
            GROUP BY employee_id) x
    ON job_history.employee_id = x.employee_id
JOIN (SELECT employee_id, min(start_date) as min_start
            FROM hr.job_history
            GROUP BY employee_id) y
    ON job_history.employee_id = y.employee_id;