DECLARE @SID INT
    DECLARE @descr varchar(255)
    DECLARE @item varchar(255)

    DECLARE cDetailsCursor CURSOR
    READ_ONLY
    FOR 

	select csg.CID
	from table1 csg
	JOIN table2 map
	ON map.ID = csg.ID
	WHERE map.SID = @SID

	union 
	
	select cs.CID
	FROM table3 cs
	where cs.SID = @SID

    OPEN cDetailsCursor

    SET @descr = ''

    FETCH NEXT FROM cDetailsCursor INTO @item

    WHILE (@@fetch_status <> -1)

        BEGIN
    
            IF (@@fetch_status <> -2)
            BEGIN
                IF Len(@descr) = 0 
                BEGIN
                    SET @descr = @item
                END
                ELSE
                BEGIN
                    SET @descr = @descr + ', ' + @item
                END
                    
            END

            FETCH NEXT FROM cDetailsCursor INTO @item
        END

    CLOSE cDetailsCursor
    DEALLOCATE cDetailsCursor

    RETURN(@descr)

SET @MyVariable = ''

SELECT @MyVariable = @MyVariable + ', ' + MyColumn
FROM MyTable
ORDER BY MyKeyColumn

-- Remove leading comma
SET @MyVariable = RIGHT(@MyVariable ,LEN(@MyVariable )-1)

SELECT @MyVariable 

WITH CTE AS
(
SELECT
        name as TableName,
        object_id
  FROM sys.tables WHERE schema_id = schema_id('dbo')
)
SELECT TableName,
       CommaList = STUFF((
                   SELECT ',' + c.name
                   FROM sys.columns c
                   WHERE c.object_id = CTE.object_id
                   ORDER BY c.column_id
                       FOR XML PATH(''),TYPE).value('.','varchar(max)'),1,1,'')
  FROM CTE
 ORDER BY Tablename;

	DECLARE @descr VARCHAR(MAX) = '', @SID INT = 10
	;WITH CTE AS
	(
	SELECT 
		csg.CID
	FROM 
		table1 csg
	JOIN 
		table2 map
		ON 
		map.PID = csg.PID
	WHERE 
		map.SID = @SID
	UNION 
	SELECT 
		cs.CID
	FROM 
		table3 cs
	WHERE 
		cs.SID = @SID
	),
	CTE2 AS(
	SELECT CommaList = STUFF((
                   SELECT ', ' + CONVERT(VARCHAR,c.CID)
                   FROM CTE c
                   ORDER BY c.ID
                       FOR XML PATH(''),TYPE).value('.','varchar(max)'),1,2,'')
  FROM CTE
 )
 SELECT @descr = CommaList FROM CTE2 GROUP BY CommaList
 
 RETURN (@descr)