c# - How to query for items that don't exist by date

Question

I have a one to many relationship between campaigns and campaign stats. A campaign stat item can have at most one entry in the database for a campaign for a single day.

So starting from 9/20/13 - DateTime.Now get campaigns where there isn't a related campaign stat, but I also want to get the actual date that the stat is missing from

I'd like to display for instance campaign name, stat date(that is missing). I'm having a hard time coming up with a solution to this, but I've written this code to start.

        var fromDate = new DateTime(2013, 9, 20);
        var toDate = DateTime.Now;
        var dates = Enumerable.Range(0, toDate.Subtract(fromDate).Days + 1)
            .Select(d => fromDate.AddDays(d));

        var a = from c in _db.Campaigns
            join s in _db.CampaignStats on c.Id equals s.CampaignId into s1
            from s in s1.DefaultIfEmpty()
            where s == null
            select new {c, s};

Sample output would be: (Campaign 1 has stats for 9/20/2013 and 9/22/2013)

`Campaign 1 9/21/2013`
`Campaign 1 9/23/2013`
`Campaign 1 9/24/2013`
`...`

Edit

Using Bob's answer I formed this LINQ query:

           (from counts in
                (from cal in _db.CalendarMonths
                 from c in _db.Campaigns
                 let statCount = (from s in _db.CampaignStats
                                  where s.CampaignId == c.Id
                                  where s.Date == cal.date
                                  group s by s.Id into s1
                                  select s1.Count()).FirstOrDefault()
                 select new
                        {
                            cal.date,
                            c.Id,
                            statCount
                        })
            where counts.statCount == 0
            select new
                   {
                       counts.Id,
                       counts.date,
                   });

Answer 1

It's ugly with recursion but:

SELECT
    counts.CalDate,
    counts.CampaignId,
FROM
    (SELECT
         cal.[Date] as CalDate,
         c.CampaignId,
         (SELECT COUNT(*) FROM CampaignStats WHERE CampaignID = c.CampaignId AND StatDate = cal.[Date]) AS StatCount
    FROM 
    CalendarMonths cal, Campaigns c) counts
WHERE
    counts.StatCount = 0