select 
	(
		select 
			MAX(_Date)
		from
			dbo.DimDates
		where
			dbo.DimDates.IsWorkDay = 1 and
			dbo.DimDates._Date < HollidayDates._Date
	) as PrevWorkingDay
from 
	dbo.DimDates as HollidayDates
where
	[DayNumberOfMonth] = 1 and
	IsWorkDay = 0

DC.DimDates.Where(i => i.DayNumberOfMonth == 1 && !i.IsWorkDay)
                            .Select(c => new
                            {
                                D = DC.DimDates.Where(i => i.IsWorkDay && i._Date < c._Date)
                                                            .Select(j => j._Date)
                                                            .Max()
                            }).Where(h => h.D == Дата).SingleOrDefault() != null