Duplicating Results when using Subquery, need to filter out Nulls and only show value if value exists - sql-server-2012

Question

(Edited) I am having a problem with duplicating results when using a Count() Function and then Grouping by a column that changes from Null to having a value. See Below:
Here is a sample table of data:
t_order_table
Line# Order User_Assigned
1 12345 Null
2 12345 Null
3 12345 Null
4 12345 Null
5 12345 Null
6 12345 Null
7 12345 Null
8 12345 Null
9 12345 Null
1 11223 Null
2 11223 Null
3 11223 Null
Here is the script to report on the table(below):
Select Order,
(Select Count(Line#) from t_order_table ord
Where User_Assigned is null
and o.Order = ord.Order) as 'Open Lines',
(Select Count(Line#) from t_order_table ord
Where User_Assigned is not null
and o.Order = ord.Order) as 'Picked Lines',
(Select User_Assigned from t_order_table ord
Where o.Order = ord.Order) as 'User Assigned'
from t_order_table o
Group By Order, User_Assigned
Which Returns:
Order Open Lines Picked Lines User_Assigned
12345 9 0 Null
11223 3 0 Null
As a worker logs into the system, he gets assigned to the lines, one by one as he picks the order. After he picks 3 lines, the table would look like this:
t_order_table
Line# Order User_Assigned
1 12345 Chris
2 12345 Chris
3 12345 Chris
4 12345 Null
5 12345 Null
6 12345 Null
7 12345 Null
8 12345 Null
9 12345 Null
1 11223 Null
2 11223 Null
3 11223 Null
and the report would look like this:
Order Open Lines Picked Lines User_Assigned
12345 9 3 Null
12345 9 3 Chris
11223 3 0 Null
The Result has a duplicated record because the SubSelect Query for 'User_Assigned' found a null and a user, so there is two records. I would like there to be some logic that checks if a user is assigned, it returns the user, else returns null. I can't figure out how to do that. Thanks for the help!!!!

Answer 1

This seems to give you what you need.
set transaction isolation level read uncommitted;
declare #OrderTable as table
(
[Line] tinyint,
[Order] int,
[User_Assigned] nvarchar(50)
);
insert into #OrderTable
(
[Line],
[Order],
[User_Assigned]
)
values
(1, 12345, 'Chris'),
(2, 12345, 'Chris'),
(3, 12345, 'Chris'),
(4, 12345, null),
(5, 12345, null),
(6, 12345, null),
(7, 12345, null),
(8, 12345, null),
(9, 12345, null),
(1, 11223, null),
(2, 11223, null),
(3, 11223, null);
select
o.[Order],
sum(iif(o.User_Assigned is null, 1, 0)) as [OpenLines],
sum(iif(o.User_Assigned is not null, 1, 0)) as [PickedLines],
max(o.User_Assigned) as [User_Assigned]
from #OrderTable as [o]
group by
o.[Order]
Returns:
Order OpenLines PickedLines User_Assigned
11223 3 0 NULL
12345 6 3 Chris