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我是 linq to sql 的初学者，我想知道内部连接中选择的语法是什么：

 inner join ( select CCL_TMA_ID as SecurityIdMax ,
                                max(CCL_DATE) as DateMax
                         from   dbo.usrCOURSCLOTURE
                         where  CCL_DONNEE is not null
                                and CCL_DATE <= @d
                         group by CCL_TMA_ID
                       )

完整查询：

 declare @d datetime
 select @d = getdate()

 select t0.CCL_TMA_ID as SecurityId ,
        t0.CCL_DATE as Date ,
        t0.CCL_DONNEE as Price ,
        t1.CCL_DONNEE as CurrencyPrice
 from   dbo.usrCOURSCLOTURE as t0
        inner join dbo.usrCOURSCLOTURE as t1 on t0.CCL_DEV_DONNEE = t1.CCL_TMA_ID
                                                and t0.CCL_DATE = t1.CCL_DATE
                                                and t1.CCL_DONNEE is not null

        inner join ( select CCL_TMA_ID as SecurityIdMax ,
                            max(CCL_DATE) as DateMax
                     from   dbo.usrCOURSCLOTURE
                     where  CCL_DONNEE is not null
                            and CCL_DATE <= @d
                     group by CCL_TMA_ID
                   ) cMax on t0.CCL_TMA_ID = SecurityIdMax
                             and t0.CCL_DATE <= DateMax
                             and t0.CCL_DATE >= DateMax-10
where t0.CCL_DATE > dateadd(year,-1,@d)
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2 回答 2

2

我在下面为您做了一个查询，其中包含一些解释一些功能的评论。请注意，您不能基于 <= 进行多条件连接，例如

on t0.CCL_TMA_ID = SecurityIdMax
                             and t0.CCL_DATE <= DateMax
                             and t0.CCL_DATE >= DateMax-10

你必须在第一个条件下加入，然后用 where 过滤掉它们

例如

Datetime d = Datetime.Now;
Datetime lastYear = d.AddYears(-1);
var q = from t0 in db.usrCOURSCLOTURE
        join t1 in db.usrCOURSCLOTURE.where(z => z.CCL_DONNEE.HasValue) 
        on new {a = t0.CCL_DEV_DONNEE, b = t0.CCL_DATE} equals new {a = t1.CCL_TMA_ID, b = t1.CCL_DATE}
            // the above is how to do a join on multiple conditions
        join t2 in (
            from x0 in db.usrCOURSCLOTURE.where(z => z.CCL_DONNEE.HasValue && z.CCL_DATE < d)
            .GroupBy(z => z.CCL_TMA_ID)
            select new {SecurityIdMax = x0.Key, DateMax = x0.Max(z => z.CCL_DATE)}
            //this is how you get your groupby subquery
        )
        on t0.CCL_TMA_ID equals t2.SecurityIdMax
        where
          t0.CCL_DATE  > lastYear
          && t0.CCL_DATE <= t2.DateMax
          && t0.CCL_DATE >= SqlFunctions.DateAdd("DAY", -10, t2.DateMax) //nb not sure on the interval - correct this!
        select new {SecurityId = t0.CCL_TMA_ID,
                    Date = t0.CCL_DATE,
                    Price = t0.CCL_DONNEE,
                    CurrencyPrice = t1.CCL_DONNEE};

另请注意，“SqlFunctions”类位于 System.Data.Entity 程序集中的命名空间 System.Data.Objects.SqlClient 中。

于 2013-11-05T11:00:44.563 回答
0

通过将语句括在括号中，您可以创建一个数据子集，在您的情况下，该子集将按列dbo.usrCOURSCLOTURE分组CCL_TMA_ID。

为了更清楚，让我们以不同的方式表达：

   @subsetOfData = select CCL_TMA_ID as SecurityIdMax, max(CCL_DATE) as DateMax
                      from   dbo.usrCOURSCLOTURE
                     where  CCL_DONNEE is not null and CCL_DATE <= @d
                  group by CCL_TMA_ID

接着

select t0.CCL_TMA_ID as SecurityId ,
        t0.CCL_DATE as Date ,
        t0.CCL_DONNEE as Price ,
        t1.CCL_DONNEE as CurrencyPrice
 from   dbo.usrCOURSCLOTURE as t0
        inner join dbo.usrCOURSCLOTURE as t1 on t0.CCL_DEV_DONNEE = t1.CCL_TMA_ID
                                                and t0.CCL_DATE = t1.CCL_DATE
                                                and t1.CCL_DONNEE is not null

        inner join @subsetOfData as cMax on t0.CCL_TMA_ID = SecurityIdMax
                             and t0.CCL_DATE <= DateMax
                             and t0.CCL_DATE >= DateMax-10
where t0.CCL_DATE > dateadd(year,-1,@d)
于 2013-11-05T10:46:50.423 回答