Я определила fullchart уже вначале (строка 6)
SELECT name from (SELECT t_empl.id, name, salary, manager_id, empl_id, dept_id
FROM t_empl
LEFT OUTER JOIN t_dept
ON t_empl.id=t_dept.manager_id
LEFT OUTER JOIN t_asnmt
ON t_empl.id=t_asnmt.empl_id) as fullchart
WHERE dept_id=
(SELECT dept_id FROM fullchart
WHERE manager_id IS NULL Order By salary DESC LIMIT 1)