Looping through the cursor in T-SQL - sql-server

Question

I am creating a procedure in T-SQL:
CREATE PROCEDURE usp_QC1
AS
BEGIN
DECLARE #tablename varchar(100);
DECLARE #sfilename varchar(100);
DECLARE #rread varchar(100);
DECLARE #rwrite varchar(100);
DECLARE #sserver varchar(100);
DECLARE #dbname varchar(100);
DECLARE cur_tracking CURSOR FOR
SELECT
[TableName],
sfilename,
[RecordsRead],
[RecordsWritten],
[SQLServer],
[SQLDatabase]
FROM
[ADataTracker].[dbo].[TrackerLoadLog]
WHERE
LOWER(datagroup) LIKE '%Oracle RMS%'
AND SUBSTRING(sfilename, 1, 10) = '2022-03-16'
OPEN cur_tracking;
FETCH NEXT FROM cur_tracking INTO #tablename, #sfilename, #rread, #rwrite, #sserver, #dbname;
WHILE ##Fetch_status = 0
BEGIN
SELECT
sfilename, COUNT(*)
FROM
#sserver + '.dbo.' + #dbname
WHERE
sfilename = #sfilename
GROUP BY
sfilename
FETCH NEXT FROM cur_tracking INTO #tablename, #sfilename, #rread, #rwrite, #sserver, #dbname;
END;
CLOSE cur_tracking;
DEALLOCATE cur_tracking;
END
The cursor cur_tracking is holding the data (just showing 1 record)
---------------------------------------------------------------------------------------------------------------------------
TableName |sfilename | RecordsRead |RecordsWritten |SQLServer |SQLDatabase |
History |2022-03-16\20220316032322.dat| 5819560 |5819560 |a.stg.sql.ccaintranet.com |DataRms_Back |
So the cursor is having all the information of server, Databasename, tablename. I want to go to those each server.db.table and retrieve the information using these cursor elements:
SELECT sfilename, COUNT(*)
FROM #sserver + '.dbo.' + #dbname
WHERE sfilename = #sfilename
GROUP BY sfilename
But I get an error:
invalid column name sfilename
must declare the table variable #sserver

Answer 1

This is never going to work:
select sfilename,count(*) from #sserver+'.dbo.'+#dbname
You can't parameterize entity names like this (also database comes before schema, and you missed #tablename entirely).
Instead you can do:
DECLARE #sql nvarchar(max), #exec nvarchar(1000);
...
-- then inside the cursor:
SET #sql = N'select sfilename = #sfilename,count(*)
FROM dbo.' + QUOTENAME(#tablename)
+ N' WHERE sfilename = #sfilename;';
SET #exec = QUOTENAME(#dbname) + N'.sys.sp_executesql';
EXEC #exec #sql, N'#sfilename varchar(100)', #sfilename;
Note that all of these need to be nvarchar(128), and you can use the same DECLARE for multiple variables to lighten eye strain:
DECLARE #tablename nvarchar(128),
#sfilename nvarchar(128),
#dbname nvarchar(128);
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