当DataTable列类型为DateTime时的 现象

　　　　DataTable dt = new DataTable();
            dt.Columns.Add(new DataColumn("fldHireTime",typeof(DateTime)));
            DateTime now = DateTime.Now;
            dt.Rows.Add(now);

            //dt.Rows.Add(now.ToString());//如果这样输出为1
            object obj = dt.Compute("count(fldHireTime)", string.Format("fldHireTime='{0}' ",now) );
            Console.WriteLine(obj.ToString());

           结果输出：0

            精度问题？