Execute query stored in variable in a very specific way - sql

Question

Greetings, I have a problem as follows:
I have an SQL variable declared:
DECLARE #myVariable nvarchar(max)
a third party library set a value for this variable. To simplify, lets say that the value is as follows:
SET #myVariable = 'Select ROWGUID from MySampleTable'
Now, I want to execute the following query:
SELECT ROWGUID FROM myTable WHERE ROWGUID in (exec sp_executesql #myVariable )
However, the above statement does not work because it returns an error telling me that I can't execute stored procedure in that way. I made a workaround and this is what I wrote:
create table #temptable (ID uniqueidentifier null)
if(#myVariable is not null AND #myVariable !='') insert into #temptable exec sp_executesql #myVariable
SELECT ROWGUID FROM myTable WHERE ROWGUID in (select * from #temptable)
DROP TABLE #temptable
This works fine.However I don't think it is a good idea to use temporary table. How can I achieve the same result without necessity of creating temporary tables?
I am using SQL SERVER 2005
UPDATE
Please read what I've written where is the problem:
However, the above statement does not work because it returns an error telling me that I can't execute stored procedure in that way. I made a workaround and this is what I wrote:

Answer 1

Keep it simple
-- Your original declaration
declare #myVariable nvarchar(max)
set #myVariable = 'Select ROWGUID from MySampleTable'
-- Additional code
declare #myQuery nvarchar(max) = 'SELECT ROWGUID FROM myTable WHERE ROWGUID in (' + #myVariable + ')'
exec (#myQuery)

Answer 2

Maybe you could use User Defined Functions instead of stored procedures?

Answer 3

If you are using SQL Server 2005 or 2008, you could use a Common Table Expression instead of creating a temporary table.
Common Table Expressions
Your CTE should look like:
WITH Records (ROWGUID) AS (
SELECT ROWGUID
FROM MySimpleTable
)
Then you can simply use:
SELECT ROWGUID
FROM myTable
WHERE ROWGUID IN (SELECT ROWGUID
FROM Records);
Which potentially means you can drop your Variable.
EDIT
Ok, so CTE is out of the question. But, what about using a Table variable instead of creating a Temporary Table.
DECLARE #myVar nvarchar(max);
DECLARE #table TABLE
(
ROWGUID uniqueidentifier
)
SET #myVar = 'SELECT ROWGUID FROM MySampleTable';
INSERT INTO #table
EXEC sp_executesql #myVar;
SELECT ClientID
FROM myTable
WHERE EXISTS (SELECT ClientID FROM #table);