一表teammem存有员工工号（staff），组别（team），开始日期（effdt），结束日期（expdt），要用sql抓出当月有调职位的员工号，开始日期，结束日期，sql该如何写？自己寫的語句只能抓有部門變動，但不能准確取到具體一個月有哪些人有職位調動。先谢各位了！

select a.code, a.lname, b.effdt, b.expdt, c.lname as group0
from staff a, teammem b, team c
where a.code = b.staff
and b.team = c.code
and a.code like 'A%'
and b.staff in (select ds.staff from (select a.staff, count(a.staff)
                                      from teammem a, staff b
                                      where a.staff = b.code
                                      and b.code like 'A%'
                                      group by a.staff
                                      having count(a.staff) > 1
                                     ) ds
               )
order by a.code, b.effdt