How to use CASE WHEN in group by - sql

Question

I want to use group by for the table NRW_MONTH_DATA.
SELECT [OBJECT_ID]
,[YEAR_MONTH]
,[SELLING_AMOUNT]
,[DEFAULT_SELLING_DATA]
,[LOCK_SELLING_AMOUNT]
,[RGCB]
,[ICKZ]
,[YCKZ]
FROM [dbo].[NRW_MONTH_DATA]
IF LOCK_SELLING_AMOUNT is 0 then group by OBJECT_ID and calculate the sum of [RGCB],[ICKZ] and [YCKZ]
SELECT #SELLING_AMOUNT=(ISNULL(SUM(YCKZ),0)+ISNULL(SUM(RGCB),0)+ ISNULL(SUM(ICKZ),0))
FROM [dbo].[NRW_MONTH_DATA]
WHERE OBJECT_ID=#OBJECT_ID
AND YEAR_MONTH >=#SELLING_CENSUS_START_YM
AND YEAR_MONTH <=#SELLING_CENSUS_END_YM
GROUP BY OBJECT_ID
Now I want to add a condition that if LOCK_SELLING_AMOUNT is 1 , I need to
SELECT #SELLING_AMOUNT=ISNULL(SUM(DEFAULT_SELLING_DATA),0)
ELSE use original result to calculate the sum of the 3 columns.
I use CASE WHEN but is seems that I could not use it in group by
SELECT #SELLING_AMOUNT=
CASE LOCK_SELLING_AMOUNT WHEN 1 THEN SELLING_AMOUNT
ELSE (ISNULL(SUM(YCKZ),0)+ISNULL(SUM(RGCB),0)+ ISNULL(SUM(ICKZ),0))
END
The error is like
The column'dbo.NRW_MONTH_DATA.LOCK_SELLING_AMOUNT' in the select list is invalid because the column is not included in the aggregate function or GROUP BY clause.
Thank you in advance.
I need the group by to calculate the sum of them. Each row has an object_id and a LOCK_SELLING_AMOUNT and other columns for one month, I want to use group to calculate the sum during month span.
It works well when I do not consider the LOCK_SELLING_AMOUNT

Answer 1

First, you don't want GROUP BY. So just use:
SELECT #SELLING_WATER = (COALESCE(SUM(YCKZ), 0) + COALESCE(SUM(RGCB), 0)+ COALESCE(SUM(ICKZ), 0))
FROM [dbo].[NRW_MONTH_DATA]
WHERE OBJECT_ID=#OBJECT_ID AND
YEAR_MONTH >= #SELLING_CENSUS_START_YM
YEAR_MONTH <= #SELLING_CENSUS_END_YM;
Now, the problem is that a column can change values on different rows. So, what row does LOCK_SELLING_AMOUNT come from? We could assume it is the same on all rows. Or perhaps you want an aggregation function:
SELECT #SELLING_WATER = (CASE WHEN MAX(LOCK_SELLING_AMOUNT) = 1
THEN MAX(CASE WHEN LOCK_SELLING_AMOUNT = 1 THEN SELLING_AMOUNT END)
ELSE (COALESCE(SUM(YCKZ), 0) + COALESCE(SUM(RGCB), 0)+ COALESCE(SUM(ICKZ), 0))
END)
FROM [dbo].[NRW_MONTH_DATA]
WHERE OBJECT_ID=#OBJECT_ID AND
YEAR_MONTH >= #SELLING_CENSUS_START_YM
YEAR_MONTH <= #SELLING_CENSUS_END_YM;