Solution for SQL conditional query - sql

Question

I've been tasked with coming up with a solution for a problem that was found this morning. I have a query that I need to do some math with. I have three pertinent columns.
SELECT lQ.[QUANTITY], lQ.[FORM_FACTOR_ID], oQ.[INDIVIDUAL_PACKAGING]
FROM [dbo].[AOF_ORDER_LINE_QUEUE] as lQ
LEFT JOIN [dbo].[AOF_ORDER_QUEUE] AS oQ
ON lQ.[SALES_ORDER_NUMBER] = oQ.[SALES_ORDER_NUMBER]
I can see myself doing this in a loop easily in languages I know best. It doesn't seem that looping is a good thing to do in SQL based on some preliminary research so I am reaching out for suggestions.
I need to output a total value which is a conditional sum of lQ.[QUANTITY]. The condition is if oQ.[FORM_FACTOR_ID] is equal to 1 then the output for that particular row is equal to the value of lQ.[QUANTITY]. If oQ.[FORM_FACTOR_ID] is equal to 2 then if oQ.[INDIVIDUAL_PACKAGING] is true, then the output of that particular row in the query is equal to lQ.[QUANTITY]. If the value is false, then the output of that particular row in the query is divided by 2. The final output needs to be a single integer.
QUANTITY FORM_FACTOR_ID INDIVIDUAL_PACKAGING
4 2 1
5 1 1
I would need a query that outputs the value 7 for the above table.
QUANTITY FORM_FACTOR_ID INDIVIDUAL_PACKAGING
4 2 0
5 2 0
That same query needs to output 5 for the above table.
What would be the best way to go about doing this?

Answer 1

If I understand the question correctly, you just want conditional aggregation -- a CASE as an argument to SUM().
If I follow the logic, it would look like:
SELECT SUM(CASE WHEN oq.FORM_FACTOR_ID = 1 THEN lQ.QUANTITY
WHEN oQ.FORM_FACTOR_ID = 2 AND oQ.INDIVIDUAL_PACKAGING = 1 THEN lQ.QUANTITY
WHEN oQ.FORM_FACTOR_ID = 2 AND oQ.INDIVIDUAL_PACKAGING = 0 THEN lQ.QUANTITY / 2
END)
FROM [dbo].[AOF_ORDER_LINE_QUEUE] lQ LEFT JOIN
[dbo].[AOF_ORDER_QUEUE] oQ
ON lQ.[SALES_ORDER_NUMBER] = oQ.[SALES_ORDER_NUMBER];