How to combine GROUP BY and ROW_NUMBER?

Question

I hope following sample code is self-explanatory:

declare @t1 table (ID int,Price money, Name varchar(10))
declare @t2 table (ID int,Orders int,  Name varchar(10))
declare @relation  table (t1ID int,t2ID int)
insert into @t1 values(1, 200, 'AAA');
insert into @t1 values(2, 150, 'BBB');
insert into @t1 values(3, 100, 'CCC');
insert into @t2 values(1,25,'aaa');
insert into @t2 values(2,35,'bbb');
insert into @relation values(1,1);
insert into @relation values(2,1);
insert into @relation values(3,2);

select T2.ID AS T2ID
,T2.Name as T2Name
,T2.Orders
,T1.ID AS T1ID
,T1.Name As T1Name
,T1Sum.Price
FROM @t2 T2
INNER JOIN (
    SELECT Rel.t2ID
        ,MAX(Rel.t1ID)AS t1ID 
-- the MAX returns an arbitrary ID, what i need is: 
--      ,ROW_NUMBER()OVER(Partition By Rel.t2ID Order By Price DESC)As PriceList
        ,SUM(Price)AS Price
        FROM @t1 T1 
        INNER JOIN @relation Rel ON Rel.t1ID=T1.ID
        GROUP BY Rel.t2ID
)AS T1Sum ON  T1Sum.t2ID = T2.ID
INNER JOIN @t1 T1 ON T1Sum.t1ID=T1.ID

Result:

T2ID   T2Name   Orders  T1ID    T1Name  Price     
 1      aaa       25     2       BBB    350,00     
 2      bbb       35     3       CCC    100,00

What i need is commented above, a way to get the ROW_NUMBER but also to Group By in the first place. So i need the sum of all T1-prices grouped by T2.ID in the relation-table and in the outer query the t1ID with the highest price.

In other words: How to change MAX(Rel.t1ID)AS t1ID to somewhat returning the ID with the highest price?

So the desired result is(notice that first T1ID changed from 2 to 1 since it has the higher price):

T2ID   T2Name   Orders  T1ID    T1Name  Price     
 1      aaa       25     1       AAA    350,00     
 2      bbb       35     3       CCC    100,00

Note : in case you're wondering why i don't multiply Orders with Price: they are not realated(so i should have left off this column since it's a bit ambiguous, please ignore it, i've just added it to make all less abstract). Actually Orders must remain unchanged, that's the reason for the sub-query approach to join both and the reason why i need to group by in the first place.

Conclusion : obviously the core of my question can be answered by the OVER clause that can be applied to any aggregate function like SUM (see Damien's answer ) what was new to me. Thank you all for your working approaches.

Answer 1

Wow, the other answers look complex - so I'm hoping I've not missed something obvious.

You can use OVER / PARTITION BY against aggregates, and they'll then do grouping/aggregating without a GROUP BY clause. So I just modified your query to:

select T2.ID AS T2ID
    ,T2.Name as T2Name
    ,T2.Orders
    ,T1.ID AS T1ID
    ,T1.Name As T1Name
    ,T1Sum.Price
FROM @t2 T2
INNER JOIN (
    SELECT Rel.t2ID
        ,Rel.t1ID
 --       ,MAX(Rel.t1ID)AS t1ID 
-- the MAX returns an arbitrary ID, what i need is: 
      ,ROW_NUMBER()OVER(Partition By Rel.t2ID Order By Price DESC)As PriceList
        ,SUM(Price)OVER(PARTITION BY Rel.t2ID) AS Price
        FROM @t1 T1 
        INNER JOIN @relation Rel ON Rel.t1ID=T1.ID
--        GROUP BY Rel.t2ID
)AS T1Sum ON  T1Sum.t2ID = T2.ID
INNER JOIN @t1 T1 ON T1Sum.t1ID=T1.ID
where t1Sum.PriceList = 1

Which gives the requested result set.

Answer 2

Undoubtly this can be simplified but the results match your expectations.

The gist of this is to

• Calculate the maximum price in a seperate CTE for each t2ID
• Calculate the total price in a seperate CTE for each t2ID
• Combine the results of both CTE 's

SQL Statement

;WITH MaxPrice AS ( 
    SELECT  t2ID
            , t1ID
    FROM    (       
                SELECT  t2.ID AS t2ID
                        , t1.ID AS t1ID
                        , rn = ROW_NUMBER() OVER (PARTITION BY t2.ID ORDER BY t1.Price DESC)
                FROM    @t1 t1
                        INNER JOIN @relation r ON r.t1ID = t1.ID        
                        INNER JOIN @t2 t2 ON t2.ID = r.t2ID
            ) maxt1
    WHERE   maxt1.rn = 1                            
)
, SumPrice AS (
    SELECT  t2ID = t2.ID
            , Price = SUM(Price)
    FROM    @t1 t1
            INNER JOIN @relation r ON r.t1ID = t1.ID
            INNER JOIN @t2 t2 ON t2.ID = r.t2ID
    GROUP BY
            t2.ID           
)           
SELECT  t2.ID
        , t2.Name
        , t2.Orders
        , mp.t1ID
        , t1.ID
        , t1.Name
        , sp.Price
FROM    @t2 t2
        INNER JOIN MaxPrice mp ON mp.t2ID = t2.ID
        INNER JOIN SumPrice sp ON sp.t2ID = t2.ID
        INNER JOIN @t1 t1 ON t1.ID = mp.t1ID

Answer 3

;with C as
(
  select Rel.t2ID,
         Rel.t1ID,
         t1.Price,
         row_number() over(partition by Rel.t2ID order by t1.Price desc) as rn
  from @t1 as T1
    inner join @relation as Rel
      on T1.ID = Rel.t1ID
)
select T2.ID as T2ID,
       T2.Name as T2Name,
       T2.Orders,
       T1.ID as T1ID,
       T1.Name as T1Name,
       T1Sum.Price
from @t2 as T2
  inner join (
              select C1.t2ID,
                     sum(C1.Price) as Price,
                     C2.t1ID
              from C as C1
                inner join C as C2 
                  on C1.t2ID = C2.t2ID and
                     C2.rn = 1
              group by C1.t2ID, C2.t1ID
             ) as T1Sum
    on T2.ID = T1Sum.t2ID
  inner join @t1 as T1
    on T1.ID = T1Sum.t1ID

Answer 4

The deduplication (to select the max T1) and the aggregation need to be done as distinct steps. I've used a CTE since I think this makes it clearer:

;WITH sumCTE
AS
(
    SELECT  Rel.t2ID, SUM(Price) price
    FROM    @t1         AS T1
    JOIN    @relation   AS Rel 
    ON      Rel.t1ID=T1.ID
    GROUP 
    BY      Rel.t2ID
)
,maxCTE
AS
(
    SELECT  Rel.t2ID, Rel.t1ID, 
            ROW_NUMBER()OVER(Partition By Rel.t2ID Order By Price DESC)As PriceList
    FROM    @t1         AS T1
    JOIN    @relation   AS Rel 
    ON      Rel.t1ID=T1.ID
)
SELECT T2.ID AS T2ID
,T2.Name as T2Name
,T2.Orders
,T1.ID AS T1ID
,T1.Name As T1Name
,sumT1.Price
FROM    @t2 AS T2
JOIN    sumCTE AS sumT1
ON      sumT1.t2ID = t2.ID
JOIN    maxCTE AS maxT1
ON      maxT1.t2ID = t2.ID
JOIN    @t1 AS T1
ON      T1.ID = maxT1.t1ID
WHERE   maxT1.PriceList = 1