TestScript.sql

SELECT
   [Name], *
FROM
   Customer AS c 
   inner join
      Purchaise AS p 
      ON c.CustomerId = p.CustomerId 
WHERE
   p.ProductNameN = N'Молоко' 
   and c.CustomerId not in 
   (
	  SELECT
         CustomerId 
      FROM
         Purchaise 
      WHERE
         datepart(m, PurchaiseDatetime) = datepart(m, dateadd(m, - 1, getdate())) 
         AND datepart(yyyy, PurchaiseDatetime) = datepart(yyyy, dateadd(m, - 1, getdate())) 
         and ProductNameN = N'Сметана'
   )