Subqueries in MSSQL producing NULL values - sql

Question

I am trying to determine my store only accounts revenue from the database, to do this I need to look through all account numbers with revenue against a 'store' description who do NOT appear in a list of accounts with an 'online' description which I have tried todo in the subquery below. The query runs however it just returns NULL values in my store_only_revenue column. Any guidance on what to do from here would be appreciated. Am I approaching the problem in a good way? Or is there a better solution:
SELECT
town,
financial_pd as month,
SUM(CASE WHEN [Descr] = 'online' THEN Net_Revenue ELSE 0 END) as online_revenue,
SUM(CASE WHEN [Descr] = 'store' THEN Net_Revenue ELSE 0 END) as store_revenue,
COUNT(DISTINCT CASE WHEN [Descr] = 'online' THEN Account_Number ELSE NULL END) as online_accounts,
COUNT(DISTINCT CASE WHEN [Descr] = 'store' THEN Account_Number ELSE NULL END) as store_accounts,
(SELECT
SUM(Net_Revenue)
FROM [mydb].[dbo].[mytable]
WHERE
Descr = 'store'
AND Account_Number
NOT IN(
SELECT DISTINCT Account_Number
FROM [mydb].[dbo].[mytable]
WHERE
Descr = 'online')
) as store_only_revenue
FROM [mydb].[dbo].[mytable] as orders
WHERE
Group_name = 'T'
AND NOT
Type_name_1 = 'Electronic'
AND
Account_type <> 1
AND
Total_Value > 0
AND
(Insert_Date BETWEEN '2016-05-30' AND '2016-07-03'
OR
Insert_Date BETWEEN '2015-05-25' AND '2015-06-28')
OR
(Insert_Date BETWEEN '2016-05-30' AND '2016-07-03'
AND
Insert_Date BETWEEN '2015-05-25' AND '2015-06-28')
GROUP BY
town,
financial_pd as period

Answer 1

This expression is suspect:
Account_Number NOT IN (SELECT DISTINCT t.Account_Number
FROM [mydb].[dbo].mytable t
WHERE t.Descr = 'online'
)
Assuming that the syntax problems are typos (missing table name, desc is a reserved word), then this will never return true if even one Account_Number is NULL. One way to fix this is:
Account_Number NOT IN (SELECT t.Account_Number
FROM [mydb].[dbo].mytable t
WHERE t.Desc = 'online' AND t.Account_Number IS NOT NULL
)
I would use NOT EXISTS:
not exists (select 1
from [mydb].[dbo].??? x
where x.Desc = 'online' AND ??.Account_Number = x.Account_Number
)
You need to use proper table aliases for this to work. Either of these solutions may fix your problem.