SQL Server Aggregation Using Partitioning - sql-server

Question

I have been trouble writing a SQL query to roll up multiple balances based on a similar ID group and display the balance against products with a flag of N. I imagine I need to use a partition function or a max funcction to do this.
The desired results are in the table below underneath the sample dataset. Would anyone have a fix for this available?
Would anyone know logic to help for this? Basically I need to group everything by the ID and where there is a flag of N roll the balances up to that record, if there is no record with a flag of N we just aggregate by pdct_Type_C.
SELECT
Client,
SUM(Limit) Limit,
SUM(Balance) Balance,
SUM(Exposure) Exposure,
MAX(CASE WHEN Flag = 'N' THEN Pdct_type_c ELSE NULL END) Pdct_type_c,
ID
FROM Table
GROUP BY Client, ID
SAMPLE DATASET
Client | Limit | Balance | Exposure | Pdct_type_c | Flag | ID
--------------------------------------------------------------------------------
John | 60,000,000.00| - | 5,000,000| DERIV | N | 2
John | - | 1,000,000.00 | - | FX | y | 2
John | - | 2,000,000.00 | - | IC | y | 2
John | 1,000,000.00 | 3,000,000.00 | - | DCO | y | 3
John | 1,000,000.00 | 3,000,000.00 | - | DCO | y | 3
CURRENT RESULTS
Client | Limit | Balance | Exposure | Pdct_type_c | Flag | ID
--------------------------------------------------------------------------------
John | 60,000,000.00| 3,000,000.00 | 5,000,000| DERIV | N | 2
John | 2,000,000.00 | 6,000,000.00 | - | NULL | Y | 3
DESIRED RESULTS
Client | Limit | Balance | Exposure | Pdct_type_c | Flag | ID
--------------------------------------------------------------------------------
John | 60,000,000.00| 3,000,000.00 | 5,000,000| DERIV | N | 2
John | 2,000,000.00 | 6,000,000.00 | - | DCO | Y | 3

Answer 1

It is entirely possible that this is doable with a windowing function. However here is the old fashioned way of doing it
This shows us just the records that have an N entry
SELECT
ID,
MIN(Pdct_type_c) Pdct_type_c
FROM Table
WHERE Flag = 'N'
GROUP BY ID
This outer joins to it to decide what to group on
SELECT
T.Client,
SUM(T.Limit) Limit,
SUM(T.Balance) Balance,
SUM(T.Exposure) Exposure,
ISNULL(N.Pdct_type_c, T.Pdct_type_c) Pdct_type_c
CASE WHEN N.Pdct_type_c IS NULL THEN T.Flag ELSE 'N' END Flag,
T.ID
FROM Table T
LEFT OUTER JOIN
(
SELECT
ID,
MIN(Pdct_type_c) Pdct_type_c
FROM Table
WHERE Flag = 'N'
GROUP BY ID
) N
ON T.ID = N.ID
GROUP BY T.Client, T.ID,
ISNULL(N.Pdct_type_c, T.Pdct_type_c),
CASE WHEN N.Pdct_type_c IS NULL THEN T.Flag ELSE 'N' END