Trying to strip out values from a column based on another columns and store that value to be used in a calculation - sql

Question

I am somewhat a novice at t-sql. I'm having trouble getting incorporating row values into a variables based on another columns value.
The database table has a single quantity field where all the quantity amounts are stored as positive amounts. There is a separate column that represents the direction of the transaction. A direction of 1 means it's inbound. A direction of -1 means it's inbound. Netting the inbound qty against the outbound provides the net remaining quantity.
I've been able to segregate inbound and outbound into separate columns. I've aliased each column (InQty and OutQty) to give the reader the proper context. The last thing I need is to net the two amounts (i.e. InQty minus OutQty) into another column labelled NetQty. I've tried to use variables, with and without a case statement but nothing I've tried is working. I fell like I'm real close but just can't seem to get the proper structure to the query.
The output I'm trying to get is:
ItemID ItemPartNumber InQty OutQty NetQty
1140797106360931 ACRFCO 5.000000 2.000000
Below is the query I've developed so far.
The comment lines are there to me assist in developing the query.
Select convert(varchar(max), i.itemid) as ItemID
,ItemPartNumber As ItemPartNumber
,Sum(case when Direction = 1 Then TransactionQty end) As InQty
,Sum(case when Direction = -1 Then TransactionQty end) as OutQty
FROM InventoryTransaction IT
join item i on i.itemid = it.ItemID
group by i.itemid, it.ItemPartNumber
Order by it.ItemPartNumber

Answer 1

I think you want:
select i.itemid, i.ItemPartNumber,
Sum(case when Direction = 1 Then TransactionQty end) As InQty,
Sum(case when Direction = -1 Then TransactionQty end) as OutQty,
sum(case when Direction = 1 then TransactionQty
when Direction = -1 then TransactionQty
end) as netqty
from InventoryTransaction IT i
item i
on i.itemid = it.ItemID
group by i.itemid, it.ItemPartNumber
order by it.ItemPartNumber;
I see no reason to convert the first value to a string, so I removed the conversion.
Assuming that direction only takes on the values -1 and 1 (and perhaps 0 and NULL), you can simplify this to:
select i.itemid, i.ItemPartNumber,
sum(case when Direction = 1 Then TransactionQty end) As InQty,
sum(case when Direction = -1 Then TransactionQty end) as OutQty,
sum(Direction * TransactionQty) as netqty
from InventoryTransaction IT i
item i
on i.itemid = it.ItemID
group by i.itemid, it.ItemPartNumber
order by it.ItemPartNumber

Answer 2

I think a good way to avoid further comparisons, sums or other operations and get better performance could be to use your query as a subquery:
SELECT ItemID, ItemPartNumber, InQty, OutQty, InQty-OutQty AS NetQty FROM(
/* Start of your query */
Select convert(varchar(max), i.itemid) as ItemID
,ItemPartNumber As ItemPartNumber
,Sum(case when Direction = 1 Then TransactionQty end) As InQty
,Sum(case when Direction = -1 Then TransactionQty end) as OutQty
FROM InventoryTransaction IT
join item i on i.itemid = it.ItemID
group by i.itemid, it.ItemPartNumber
Order by it.ItemPartNumber
/* End of your query */
) AS T;