Question

将DATENAME（）函数添加到查询会导致重复行，尽管“distinct”。

TREE - TreeId, CityId, DatePlanted
WATER - WaterId, TreeId(fk), DateWatered

表1是表2中的一对多

TREE表中的每一行都表示植树。水表是浇灌那棵树的一个例子。一棵树一年浇水多次。你明白了。

我需要返回一份报告，显示种植的树木数量，按月份和浇水的次数。

SELECT t.CityId
        , COUNT(distinct t.TreeId) as 'Trees Planted'
        , COUNT(w.TreeId) as 'Trees Watered'        
FROM TREE t
JOIN WATER w ON t.TreeId = w.TreeId
WHERE w.DateWatered between @Start AND @End
GROUP BY t.CityId

这很好用。然而，当我尝试按月分组时，t.Treeid不再明显，因此树的数量太高。

SELECT t.CityId
    , DATENAME(month, w.DateWatered)
        , COUNT(distinct t.TreeId) as 'Trees Planted'
        , COUNT(w.TreeId) as 'Trees Watered'        
FROM TREE t
JOIN WATER w ON t.TreeId = w.TreeId
WHERE w.DateWatered between @Start AND @End
GROUP BY t.CityId, DATENAME(month, w.DateWatered)

编辑：我发现为什么我会得到重复但不知道如何修复它。如果一棵树在2016年4月浇灌，那么在2016年5月再次浇灌，我得到了种植的2棵树和2棵树浇灌的地方应该是一棵树种植和2次浇水。如果我在没有返回日期的情况下进行第一次查询，我会得到正确的数字。因此，通过添加日期，即使我按年份分组，然后按月分组，同一树的两次浇水，它也显示两次种植的树。我目前正在研究使用CTE来保持查询的每个部分分开。

Answer 1

   SELECT t.CityId
       , ISNULL(DATENAME(month, w.DateWatered), DATENAME(month, t.DatePlanted))
       , (SELECT COUNT(tDistinct.TreeId) FROM TREE tDistinct 
        WHERE tDistinct.TreeId = t.TreeId AND DATENAME(month, tDistinct.DatePlanted) = DATENAME(month, t.DateWatered) AND t.DatePlanted between @Start AND @End) as 'Trees Planted'
      , COUNT(w.TreeId) as 'Trees Watered'        
     FROM TREE t
     JOIN WATER w ON t.TreeId = w.TreeId
    WHERE w.DateWatered between @Start AND @End
    GROUP BY t.CityId, DATENAME(month, w.DateWatered), DATENAME(month, t.DatePlanted)

这里唯一的缺点是这样一个场景，在一个月里没有树被种植，树上种植的日期将为空，所以我添加了一个检查...不确定你的数据是什么样的，这样它可能会使感觉忽略ISNULL检查以支持原始分组

EDITED：根据您的要求，我不认为CTE是必要的;根据您提供的其他信息，我已稍微更改了查询以满足您的需求：

   `SELECT DATENAME(MONTH, myConsolidatedTree.DateAction) as myDate
          ,(SELECT COUNT(*) 
               FROM TREE AS t
          WHERE 
            DATENAME(MONTH, myConsolidatedTree.DateAction) = DATENAME(MONTH, t.DatePlanted)
           ) as myNumberOfPlanted
           ,(SELECT COUNT(*) 
               FROM WATER AS w 
            WHERE 
                DATENAME(MONTH, myConsolidatedTree.DateAction) = DATENAME(MONTH, w.DateWatered)
                    ) as myNumberOfWatered

        FROM(
            SELECT t.DatePlanted as DateAction
                   ,t.TreeId as IdAction
                   ,'PLANTED' as TreeAction
                FROM TREE t

            UNION

            SELECT w.DateWatered as DateAction
                   ,w.TreeId as IdAction
                   ,'WATERED' as TreeAction
                FROM WATER w) as myConsolidatedTree
    WHERE myConsolidatedTree.DateAction between @StartDate and @EndDate
    GROUP BY DATENAME(MONTH, myConsolidatedTree.DateAction), DATEPART(MONTH, myConsolidatedTree.DateAction)
    ORDER BY DATEPART(MONTH, myConsolidatedTree.DateAction)`

虽然统一子查询包含的信息多于此问题所需的信息，但我将其他TreeId和派生的TreeAction列保留在那里，以防您将来遇到此需要。

Answer 2

这演示了如何将问题分解为公共表表达式（CTE）中的步骤。请注意，您可以使用其中一个注释select替换最终select以查看中间结果。它是测试，调试或理解正在发生的事情的便捷方式。

您遇到的一个问题是尝试仅根据浇水日期汇总数据。如果在一个没有浇水的月份种植一棵树，那么它就不会被计算在内。下面的代码总结了日期范围内的种植和浇水，然后将它们组合成一个结果集。

-- Sample data.
declare @Trees as Table ( TreeId Int Identity, CityId Int, DatePlanted Date );
declare @Waterings as Table ( WateringId Int Identity, TreeId Int, DateWatered Date );
insert into @Trees ( CityId, DatePlanted ) values
  ( 1, '20160115' ), ( 1, '20160118' ),
  ( 1, '20160308' ), ( 1, '20160318' ), ( 1, '20160118' ),
  ( 1, '20170105' ),
  ( 1, '20170205' ),
  ( 1, '20170401' ),
  ( 2, '20160113' ), ( 2, '20160130' ),
  ( 2, '20170226' ), ( 2, '20170227' ), ( 2, '20170228' );
insert into @Waterings ( TreeId, DateWatered ) values
  ( 1, '20160122' ), ( 1, '20160129' ), ( 1, '20160210' ), ( 1, '20160601' ),
  ( 5, '20160120' ), ( 5, '20160127' ), ( 5, '20160215' ), ( 5, '20160301' ), ( 5, '20160515' );
select * from @Trees;
select * from @Waterings;

-- Combine the data.
declare @StartDate as Date = '20100101', @EndDate as Date = '20200101';
with
  -- Each tree with the year and month it was planted.
  TreesPlanted as (
    select CityId, TreeId,
      DatePart( year, DatePlanted ) as YearPlanted,
      DatePart( month, DatePlanted ) as MonthPlanted
      from @Trees
      where @StartDate <= DatePlanted and DatePlanted <= @EndDate ),
  -- Tree plantings summarized by city, year and month.
  TreesPlantedSummary as (
    select CityId, YearPlanted, MonthPlanted, Count( TreeId ) as Trees
      from TreesPlanted
      group by CityId, YearPlanted, MonthPlanted ),
  -- Each watering and the year and month it occurred.
  TreesWatered as (
    select CityId, W.TreeId,
      DatePart( year, W.DateWatered ) as YearWatered,
      DatePart( month, W.DateWatered ) as MonthWatered
      from @Trees as T left outer join
        @Waterings as W on W.TreeId = T.TreeId
      where @StartDate <= W.DateWatered and W.DateWatered <= @EndDate ),
  -- Waterings summarized by city, year and month.
  TreesWateredSummary as (
    select CityId, YearWatered, MonthWatered,
      Count( distinct TreeId ) as Trees, Count( TreeId ) as Waterings
      from TreesWatered
      group by CityId, YearWatered, MonthWatered )
  -- Combine the plantings and waterings for the specified period.
  select Coalesce( TPS.CityId, TWS.CityId ) as CityId,
    Coalesce( TPS.YearPlanted, TWS.YearWatered ) as Year,
    Coalesce( TPS.MonthPlanted, TWS.MonthWatered ) as Month,
    Coalesce( TPS.Trees, 0 ) as TreesPlanted,
    Coalesce( TWS.Trees, 0 ) as TreesWatered,
    Coalesce( TWS.Waterings, 0 ) as Waterings
    from TreesPlantedSummary as TPS full outer join
      TreesWateredSummary as TWS on TWS.CityId = TPS.CityId and
      TWS.YearWatered = TPS.YearPlanted and TWS.MonthWatered = TPS.MonthPlanted
     order by CityId, Year, Month;
-- Alternative queries for testing/debugging/understanding:
--    select * from TreesPlantedSummary order by CityId, YearPlanted, MonthPlanted;
--    select * from TreesWateredSummary order by CityId, YearWatered, MonthWatered;

现在你想要在结果中包含缺失的月份（没有活动），嗯？

DATENAME导致'Distinct'被忽略

2 个答案: