Reference an ALIAS in a SUM funciton - SQL Server - sql

Question

Background:
I am trying to calculate the profit margin inside of the query and I am running into errors. When I try to use the select statement in the SUM function, I trigger an error:
Cannot perform an aggregate function on an expression containing an
aggregate or a subquery.
I understand that this is caused by having a SELECT query inside of the SUM function. From there, I tried to reference the alias of the COGS column. I recieve an error when I do that as well:
Invalid column name 'COGS'.
After messing around with the query some more, I figured it might be due to fact that I'm trying all of this inside of a SUM function and so I removed that and ran the query. It returned a few errors:
Column 'tbl_invoice.subTotal' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
Column 'tbl_invoice.tradeinAmount' is invalid in the select list because it is not contained in either an aggregate function or the
GROUP BY clause.
Column 'tbl_invoice.subTotal' is invalid in the select list because it is not contained in either an aggregate function or the
GROUP BY clause.
Column 'tbl_invoice.tradeinAmount' is invalid in the select list because it is not contained in either an aggregate function or the
GROUP BY clause.
Column 'tbl_invoice.subTotal' is invalid in the select list because it is not contained in either an aggregate function or the
GROUP BY clause.
Column 'tbl_invoice.tradeinAmount' is invalid in the select list because it is not contained in either an aggregate function or the
GROUP BY clause.
Is there another way to use or reference the value I need in the SUM function?
Query:
--Main query
SELECT
custID,
COUNT(custID) AS InvoiceNum,
--This is the column that has an alias
(SELECT cogs FROM #tempMarketing where #tempMarketing.custID = tbl_invoice.custID) as COGS,
--This is where I am trying to calculate the profit margin
SUM(((((subTotal + (-1 * tradeinAmount) - (SELECT cogs FROM #tempMarketing where #tempMarketing.custID = tbl_invoice.custID)))
/ (NULLIF(subTotal + (-1 * tradeinAmount),0))) *100)) as Profitmargin,
FROM tbl_invoice
group by custID
order by InvoiceNum desc;

Answer 1

SELECT
a.custID,
COUNT(a.custID) AS InvoiceNum, case when a.custid=b.custid then b.cogs else 0 end
as COGS,
SUM(((((subTotal + (-1 * tradeinAmount) - case when a.custid=b.custid then b.cogs else 0 end))
/ (NULLIF(subTotal + (-1 * tradeinAmount),0))) *100)) as Profitmargin,
FROM tbl_invoice a
left join #tempMarketing b on a.custID =b.custid
group by a.custID,
case when a.custid=b.custid then b.cogs else null end
order by InvoiceNum desc;

Answer 2

You can try the following query, I have created a common table expression for cogs column:
WITH cte_base AS(
SELECT cogs FROM #tempMarketing where #tempMarketing.custID = tbl_invoice.custID
)
SELECT
custID,
COUNT(custID) AS InvoiceNum,
--This is the column that has an alias
cte_base.cogs as COGS,
--This is where I am trying to calculate the profit margin
SUM(((((subTotal + (-1 * tradeinAmount) - (cte_base.cogs)))
/ (NULLIF(subTotal + (-1 * tradeinAmount),0))) *100)) as Profitmargin,
FROM tbl_invoice
group by custID
order by InvoiceNum desc;