sql - Between operator QGIS

I am using QGIS Essen version (2.14.1). I am trying to filter my data based on dates. I am wondering if the "between" operator exists like in SQL? I'm trying the following query but the results are wrong. Or is it the date format which is a problem?

(
(("all_ws_d_2"  <= '01-09-16') and  ("all_ws_d_3"   >=   '30-09-16'))
or (("all_ws_d_2"  >=  '01-09-16') and ("all_ws_d_3"  <= '30-09-16'))
or (("all_ws_d_2" <=  '01-09-16') and (("all_ws_d_3"   => '01-09-16') and ("all_ws_d_3"   <=  '30-09-16' )))
or (("all_ws_d_2" >= '01-09-16') and  (("all_ws_d_2"  <=   '30-09-16') and ("all_ws_d_3"  >=  '30-09-16')))
)