Using SQL Table Value for From Clause - sql

Question

I'm trying to write a SQL script which pulls the value of a cell in a given table across multiple databases in a single server. The table has the same name and path across several databases. I'd like to list the specific cell values in a new table.
My first step is to pull all of the database names into a temporary table and then concatenate the table path to it. The code I use is
SELECT name
INTO #dbtablepaths
FROM master.dbo.sysdatabases
WHERE name like 'FTR[0-9]%'
UPDATE #dbtablepaths
SET name=CONCAT(name, '.ftrdbo.[File]')
This will create a table of dbo paths that when queried will return the following:
__|__name_____________
1 | FTR108547.ftrdbo.[File]
2 | FTR564187.ftrdbo.[File]
3 | FTR849721.ftrdbo.[File]
I can then pull one of these dbo paths using the following query
SELECT name FROM(
SELECT ROW_NUMBER() OVER (ORDER BY name ASC) as rownumber,
name
FROM #dbtablepaths
) AS foo
WHERE rownumber = 1
This will return the first dbo path in the table which is FTR108547.ftrdbo.[File].
If I simply copy that path into a SELECT statement (see below) it will bring up the table as intended.
SELECT * FROM FTR108547.ftrdbo.[File]
However, if I try to use a subquery to enter that into the FROM clause of a SELECT statement then the query simply returns the dbo path again. E.G.
SELECT * FROM (
SELECT name FROM(
SELECT ROW_NUMBER() OVER (ORDER BY name ASC) as rownumber,
name
FROM #dbtablepaths
) AS foo
WHERE rownumber = 1
)
I would expect this query to pull the File table but instead it just returns the dbo path again. I.E. FTR108547.ftrdbo.[File]
Is there a way to use table cell values to create queries like this? I know the SELECT statement is returning a table and not a string. Is there a way to convert this table value to a string that can be used in a subsequent SELECT query?

Answer 1

you will have to forgive me as i am unable to make comments yet but you will probally want to take a look at the answers in this post
Executing SQL query on multiple databases
it has several examples that will work for you

Answer 2

This will assign the result into a variable #tabname and use it in the SELECT
DECLARE #sql VARCHAR(MAX)
DECLARE #tabname VARCHAR(100)
SELECT name
INTO #dbtablepaths
FROM master.dbo.sysdatabases
WHERE name like 'FTR[0-9]%'
UPDATE #dbtablepaths
SET name=CONCAT(name, '.ftrdbo.[File]')
SELECT #tabname = name
FROM (SELECT ROW_NUMBER() OVER (ORDER BY name ASC) AS rownumber,
name
FROM #dbtablepaths
) AS foo
WHERE rownumber = 1
SET #sql = 'SELECT * FROM ' + #tabname
EXEC(#sql)