问DATENAME导致'Distinct‘被忽略

EN

   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)

   `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)`

-- 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;