DECLARE @date  smalldatetime
DECLARE @beg_date  smalldatetime
DECLARE @end_date  smalldatetime

SELECT @beg_date ='20120701',  @end_date ='20120730'     
        
    DECLARE @tab_date TABLE (date smalldatetime UNIQUE)
    SET @date = dateadd(day,datediff(day,(0),@beg_date),(0)) 
    WHILE @date <= @end_date
    BEGIN
        INSERT INTO @tab_date VALUES (@date)
        SET @date = DATEADD(day, 1, @date)
    END
    
-- в таблице tab2 два поля даты   
    
-- Запрос 1  -- возвращает 12650 записей
SELECT q.date2,q.date3    
FROM dbo.tab2 q
        INNER JOIN @tab_date dt
        ON dt.date IN ( 
            dateadd(day,datediff(day,(0),q.date2),(0)) ,
            dateadd(day,datediff(day,(0),q.date3),(0))    
            )

-- Запрос 2  -- возвращает 9078
SELECT q.date2,q.date3    
FROM dbo.tab2 q       
WHERE EXISTS(SELECT 1 FROM @tab_date WHERE date = dateadd(day,datediff(day,(0),q.date2),(0))
OR date = dateadd(day,datediff(day,(0),q.date3),(0)))