I need to execute a requet SQL from ODOO 10

SELECT SUM(so.amount_total) as total FROM sale_order so WHERE (so.confirmation_date >= '%REF_START%' AND so.confirmation_date <= '%REF_END') AND state IN ('sale', 'done') AND user_id = %USER_ID

but the sale order that have a confirmation date at the end of the month or the beginning are not taken into account :( 

I try to execute a new requet SQL : SELECT SUM(so.amount_total) as total FROM sale_order so WHERE (so.confirmation_date >= '%REF_START% 00:00:01' AND so.confirmation_date <= '%REF_END 23:59:59') AND state IN ('sale', 'done') AND user_id = %USER_ID

But the requet doesn't work. :( I need your help our in-house developer is gone. Thank you