if window_count(attr(DATETRUNC('month', [Order Date])))>0 and min(MONTH([Order Date]))=12 and year([Order Date])=2019 then sum([Sales])-1000 else sum([Sales]) end
if window_count(attr(DATETRUNC('month', [Order Date])))>0 and min(MONTH([Order Date]))=12 and year([Order Date])=2019 then sum([Sales])-1000 else sum([Sales]) end