SELECT
*
FROM
(
SELECT
a.emp_no,
IFNULL(( SELECT MAX( salary ) FROM salaries c WHERE c.to_date='9999-01-01' and c.emp_no = a.emp_no), 0 ) -
IFNULL(( SELECT MIN( salary ) FROM salaries c WHERE c.from_date = a.hire_date and c.emp_no = a.emp_no), 0 ) AS growth
FROM
employees a
INNER JOIN salaries b ON a.emp_no = b.emp_no
where
b.to_date='9999-01-01'
) AS t1
ORDER BY
t1.growth