update T_EMPLOYEES set title_flag = (below select query TITLE_FLAG based on T_STG_LW_EMPLOYEE.Employee)

select DISTINCT T_STG_LW_EMPLOYEE.Employee,
 CASE T_STG_LW_AUMXVALUE.matrix_cat
	             WHEN  'DIR' then 'Y'
	             WHEN 'DIR2' then 'Y'
	             WHEN 'VP' then 'Y'
	             ELSE 'N'
              END as TITLE_FLAG
from T_STG_LW_EMPLOYEE
left outer join T_STG_LW_AUMXVALUE
on (ltrim(rtrim(T_STG_LW_EMPLOYEE.first_name)) + ' ' + ltrim(rtrim(T_STG_LW_EMPLOYEE.Last_name))) = 
T_STG_LW_AUMXVALUE.mx_value order by T_STG_LW_EMPLOYEE.employee

Join: T_EMPLOYEES.EMPLOYEE_NUMBER = T_STG_LW_EMPLOYEE.Employee

UPDATE T_EMPLOYEES
SET title_flag =
	CASE
		WHEN EXISTS
		(
			SELECT 1
			FROM T_STG_LW_EMPLOYEE E
			WHERE E.Employee = T_EMPLOYEES.EMPLOYEE_NUMBER
				AND EXISTS
				(
					SELECT 1
					FROM T_STG_LW_AUMXVALUE A
					WHERE A.mx_value = LTRIM(RTRIM(E.first_name)) + ' ' + LTRIM(RTRIM(E.Last_name))
						AND A.matrix_cat IN ('DIR', 'DIR2', 'VP')
				)
		)
		THEN 'Y'
		ELSE 'N'
	END;