Unable concate NULL value in SQL using CONCAT, COALESCE and ISNULL - sql-server

Question

I have a query with multiple joins where I want to combine records from two columns into one. If one column is empty then I want to show one column value as result. I tried with CONCAT, COALEASE and ISNULL but no luck. What am I missing here?
My objective is, create one column which has combination of s.Script AS Original and FromAnotherTable from query. Below query runs but throws Invalid column name 'Original' and Invalid column name 'FromAnotherTable'. when I try to use CONCAT, COALEASE or ISNULL .
SQL Query:
SELECT DISTINCT
c.Name AS CallCenter,
LTRIM(RTRIM(s.Name)) Name,
d.DNIS,
s.ScriptId,
s.Script AS Original,
(
SELECT TOP 5 CCSL.Line+'; '
FROM CallCenterScriptLine CCSL
WHERE CCSL.ScriptId = s.ScriptId
ORDER BY ScriptLineId FOR XML PATH('')
) AS FromAnotherTable,
--CONCAT(s.Script, SELECT TOP 5 CCSL.Line+'; ' FROM dbo.CallCenterScriptLine ccsl WHERE ccsl.ScriptId = s.ScriptId ORDER BY ccsl.ScriptLineId xml path(''))
--CONCAT(Original, FromAnotherTable) AS Option1,
--COALESCE(Original, '') + FromAnotherTable AS Option2,
--ISNULL(Original, '') + FromAnotherTable AS Option3,,
r.UnitName AS Store,
r.UnitNumber
FROM CallCenterScript s WITH (NOLOCK)
INNER JOIN CallCenterDNIS d WITH (NOLOCK) ON d.ScriptId = s.ScriptId
INNER JOIN CallCenter c WITH (NOLOCK) ON c.Id = s.CallCenterId
INNER JOIN CallCenterDNISRestaurant ccd WITH (NOLOCK) ON ccd.CallCenterDNISId = d.CallCenterDNISId
INNER JOIN dbo.Restaurant r WITH (NOLOCK) ON r.RestaurantID = ccd.CallCenterRestaurantId
WHERE c.Id = 5
AND (1 = 1)
AND (s.IsDeleted = 0 OR s.IsDeleted IS NULL)
ORDER BY DNIS ASC;
Output:
This works:
DECLARE #Column1 VARCHAR(50) = 'Foo',
#Column2 VARCHAR(50) = NULL;
SELECT CONCAT(#Column1,#Column2);
SELECT COALESCE(#Column2, '') + #Column1
SELECT ISNULL(#Column2, '') + #Column1
So I am not sure what I am missing in my original query.

Answer 1

Look at row 3 in the results you are getting. In your concatenated columns (Option1, 2, 3) you are getting the first script column twice. Not the first one + the second one like you expect.
The reason is because you've aliased your subquery "script" which is the same name as another column in your query, which makes it ambiguous.
Change the alias of the subquery and the problem should go away. I'm frankly surprised your query didn't raise an error.
EDIT: You can't use a column alias in another column's definition in the same level of the query. In other words, you can't do this:
SELECT
SomeColumn AS A
, (Subquery that returns a column) AS B
, A + B --this is not allowed
FROM ...
You can either create a CTE that returns the aliased columns and then concatenate them in the main query that selects from the CTE, or you have to use the original sources of the aliases, like so:
SELECT
SomeColumn AS A
, (Subquery that returns a column) AS B
, SomeColumn + (Subquery that returns a column) --this is fine
FROM ...

Answer 2

I took another approach where instead on creating separate column, I used ISNULL in my subQuery which returns my desired result.
Query:
SELECT DISTINCT
c.Name AS CallCenter,
LTRIM(RTRIM(s.Name)) Name,
d.DNIS,
s.ScriptId,
s.Script AS Original,
(
SELECT TOP 5 ISNULL(CCSL.Line, '')+'; ' + ISNULL(s.Script, '')
FROM CallCenterScriptLine CCSL
WHERE CCSL.ScriptId = s.ScriptId
ORDER BY ScriptLineId FOR XML PATH('')
) AS FromAnotherTable,
r.UnitName AS Store,
r.UnitNumber
FROM CallCenterScript s WITH (NOLOCK)
INNER JOIN CallCenterDNIS d WITH (NOLOCK) ON d.ScriptId = s.ScriptId
INNER JOIN CallCenter c WITH (NOLOCK) ON c.Id = s.CallCenterId
INNER JOIN CallCenterDNISRestaurant ccd WITH (NOLOCK) ON ccd.CallCenterDNISId = d.CallCenterDNISId
INNER JOIN dbo.Restaurant r WITH (NOLOCK) ON r.RestaurantID = ccd.CallCenterRestaurantId
WHERE c.Id = 5
AND (1 = 1)
AND (s.IsDeleted = 0 OR s.IsDeleted IS NULL)
ORDER BY DNIS ASC;

Answer 3

Here's a simplified example using table variables.
Instead of using a subquery for a field, it uses a CROSS APPLY.
And CONCAT in combination with STUFF is used to glue the strings together.
declare #Foo table (fooID int identity(1,1) primary key, Script varchar(30));
declare #Bar table (barID int identity(1,1) primary key, fooID int, Line varchar(30));
insert into #Foo (Script) values
('Test1'),('Test2'),(NULL);
insert into #Bar (fooID, Line) values
(1,'X'),(1,'Y'),(2,NULL),(3,'X'),(3,'Y');
select
f.fooID,
f.Script,
x.Lines,
CONCAT(Script+'; ', STUFF(x.Lines,1,2,'')) as NewScript
from #Foo f
cross apply (
select '; '+b.Line
from #Bar b
where b.fooID = f.fooID
FOR XML PATH('')
) x(Lines)
Result:
fooID Script Lines NewScript
----- ------- ------- -----------
1 Test1 ; X; Y Test1; X; Y
2 Test2 NULL Test2;
3 NULL ; X; Y X; Y