LINQ To SQL 中聚合函数的使用问题

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internal static object SelectDonationStatByDate(int endUserID, DateTime startDate, DateTime endDate)
    {
        GoodTreeDataContext db = new GoodTreeDataContext();
        IList<DonationStat> donationStats = new List<DonationStat>();
        DonationStat donationStat = null;

        var q = from p in db.Donation
                where p.EndUserID == endUserID
                group p by p.DonationCategory into g
                select new
                {
                    DonationCategory = g.Key,
                    TotalAmount = g.Where(i => Convert.ToDateTime(i.Date) >= startDate & Convert.ToDateTime(i.Date) <= endDate).Sum(d => d.Amount) == null ? 0 : g.Where(i => Convert.ToDateTime(i.Date) >= startDate & Convert.ToDateTime(i.Date) <= endDate).Sum(d => d.Amount)
                };

        int j = 1;
        foreach (var item in q)
        {
            donationStat = new DonationStat();
            donationStat.DonationCategory = item.DonationCategory;
            donationStat.TotalAmount = item.TotalAmount;
            donationStat.StartDate = startDate;
            donationStat.EndDate = endDate;
            donationStat.ID = j;

            donationStats.Add(donationStat);
            j++;
        }

return donationStats;
}

        var q = from p in db.Donation
                group p by p.DonationCategory into g
                select new
                {
                    DonationCategory = g.Key,
                    TotalAmount = g.Where(i => Convert.ToDateTime(i.Date) >= startDate & i.EndUserID == endUserID & Convert.ToDateTime(i.Date) <= endDate).Sum(d => d.Amount) == null ? 0 : g.Where(i => Convert.ToDateTime(i.Date) >= startDate & Convert.ToDateTime(i.Date) <= endDate).Sum(d => d.Amount)
                };

            donationStats.Add(donationStat);
            j++;
        }

return donationStats;
}

两种语句的结果有所不同，更确切的说第一种语句才能得出正确的结果。

LINQ To SQL 中 聚合函数的使用问题

LINQ To SQL 中聚合函数的使用问题