创建日期和平均值查询答案

【问题标题】：create a query for date and average values创建日期和平均值查询
【发布时间】：2012-07-09 17:12:01
【问题描述】：

我需要从数据上下文的表中选择日期和平均值，并且需要按年和月对其进行分组。在 SQL 中它看起来像这样

select Year(data) as years, Month(data) as months, Avg(value) as prices from Prices
group by Year(data),MONTH(data)
order by years, months

我创建了一个 LINQ 查询

var query0 = from c in dc.Prices
             where Convert.ToDateTime(c.data).CompareTo(left) >= 0
                   && Convert.ToDateTime(c.data).CompareTo(right) <= 0
                   && c.idsticker.Equals(x)
              group c by new { ((DateTime)c.data).Year, ((DateTime)c.data).Month }
                    into groupMonthAvg
              select groupMonthAvg;

但我不知道如何在结果中获取平均值

【问题讨论】：

标签： c# sql linq

【解决方案1】：

使用平均功能。

var query0 = from c in dc.Prices
             where Convert.ToDateTime(c.data).CompareTo(left) >= 0
                   && Convert.ToDateTime(c.data).CompareTo(right) <= 0
                   && c.idsticker.Equals(x)
              group c by new { ((DateTime)c.data).Year, ((DateTime)c.data).Month }
                    into groupMonthAvg
              select new
              {
                  years = groupMonthAvg.Key.Year,
                  months = groupMonthAvg.Key.Month,
                  prices = groupMonthAvg.Average(x=>x.value)
              };

【讨论】：

【解决方案2】：

只需在您的select 中使用Average 函数：

var query0 = from c in dc.Prices
         where Convert.ToDateTime(c.data).CompareTo(left) >= 0
               && Convert.ToDateTime(c.data).CompareTo(right) <= 0
               && c.idsticker.Equals(x)
          group c by new { ((DateTime)c.data).Year, ((DateTime)c.data).Month }
                into groupMonthAvg
          select new {
              groupMonthAvg.Key.Year, 
              groupMonthAvg.Key.Month, 
              YearAverage = groupMonthAvg.Average(x=>x.Year),
              MonthAverage = groupMonthAvg.Average(x=>x.Month)
              };

【讨论】：

【解决方案3】：

应该这样做：

var query0 = from c in dc.Prices
             where Convert.ToDateTime(c.data).CompareTo(left) >= 0
                   && Convert.ToDateTime(c.data).CompareTo(right) <= 0
                   && c.idsticker.Equals(x)
              group c by new { ((DateTime)c.data).Year, ((DateTime)c.data).Month }
                    into groupMonthAvg
              select new { Year = groupMonthAvg.Key.Year, Month = groupMonthAvg.Key.Month, Average => groupMonthAvg.Average(i => i.value) };

【讨论】：