Join with union returns me wrong result - sql

Question

I need to use union all twice. And then to join them with the same table. First union will contain a where statement and the second it will not.
Problem is that when I use the second table my result is changing.
select sum(x.quantity*x.Price)
from CustomerTrans t1
inner join (
select *
from InventoryTrans
union all
select *
from InventoryTransTemp
) x on t1.TrnDocumentID = x.TrnDocumentID
group by t1.TrnDocumentID
Here is the output from this result
First Result
Then I am adding the second union with the where statement inside
select sum(x.quantity*x.Price), sum(x2.quantity*x2.Price)
from CustomerTrans t1
left join (
select *
from InventoryTrans
union all
select *
from InventoryTransTemp
) x on t1.TrnDocumentID = x.TrnDocumentID
left join (
select *
from InventoryTrans
where printed = 2 or InvoicePaymentID = 2
union all
select *
from InventoryTransTemp
where printed = 2 or InvoicePaymentID = 2
) x2 on t1.TrnDocumentID = x2.TrnDocumentID
group by t1.TrnDocumentID
Here is the second result
Second Result
Second result it should be 3.80 and not 7.60
It look like it multiples my price *2 instead *1.

Answer 1

What happens here is that you join rows you don't want to join. Let's say your first subquery returns
+----------+-------+
| quantity | price |
+----------+-------+
| 10 | 100 |
| 10 | 200 |
+----------+-------+
for a particular document ID. And your second subquery returns only
+----------+-------+
| quantity | price |
+----------+-------+
| 10 | 200 |
+----------+-------+
The joined result is:
+------------+---------+-------------+----------+
| x.quantity | x.price | x2.quantity | x2.price |
+------------+---------+-------------+----------+
| 10 | 100 | 10 | 200 |
| 10 | 200 | 10 | 200 |
+------------+---------+-------------+----------+
And the aggregations results thereafter are:
+----------+-----------+
| x_result | x2_result |
+----------+-----------+
| 3000 | 4000 |
+----------+-----------+
instead of
+----------+-----------+
| x_result | x2_result |
+----------+-----------+
| 3000 | 2000 |
+----------+-----------+
Instead of joining single rows, you want to join aggregation results (the totals per document):
select
ct.*,
coalesce(u1.total, 0) as u1_total,
coalesce(u2.total, 0) as u2_total
from customertrans ct
left join
(
select trndocumentid, sum(quantity * price) as total
from
(
select * from inventorytrans
union all
select * from inventorytranstemp
) union1
group by trndocumentid
) u1 on u1.trndocumentid = ct.trndocumentid
left join
(
select trndocumentid, sum(quantity * price) as total
from
(
select * from inventorytrans where printed = 2 or invoicepaymentid = 2
union all
select * from inventorytranstemp where printed = 2 or invoicepaymentid = 2
) union2
group by trndocumentid
) u2 on u2.trndocumentid = ct.trndocumentid
group by ct.trndocumentid
order by ct.trndocumentid;