Order parent child records by parent group and children - sql-server

Question

I need sort query results by specific two related columns. My table is:
Row no | Col 1 | Col 2 | Col 3 | Col 4
1 | 1 | X | 1 | 5
2 | 2 | Y | 1 | 6
3 | 5 | Z | 2 | 7
4 | 6 | T | 2 | 0
5 | 7 | T | 3 | 0
6 | 6 | W | 2 | 0
The values in Col 4 represents the child record linked to Col 1.
So for Row no = 1 the next child record is row 3, where Col 1 holds the value of Col 4 from the first row.
The next child row for row 3 is row 5, based on the link between Col 1 and Col 4.
And I'd like to return this results:
Row no | Col 1 | Col 2 | Col 3 | Col 4
1 | 1 | X | 1 | 5
3 | 5 | Z | 2 | 7
5 | 7 | T | 3 | 0
2 | 2 | Y | 1 | 6
4 | 6 | T | 2 | 0
6 | 6 | W | 2 | 0
So I want the ordering to show a Parent row, followed by it's child rows, before moving on to the next top level Parent row.

Answer 1

You can achieve what you're after with a Recursive CTE to find all the parent records and link them to their child records.
Dummy table setup:
CREATE TABLE #Table1
(
[Row no] INT ,
[Col 1] INT ,
[Col 2] VARCHAR(1) ,
[Col 3] INT ,
[Col 4] INT
);
INSERT INTO #Table1
( [Row no], [Col 1], [Col 2], [Col 3], [Col 4] )
VALUES ( 1, 1, 'X', 1, 5 ),
( 2, 2, 'Y', 1, 6 ),
( 3, 5, 'Z', 2, 7 ),
( 4, 6, 'T', 2, 0 ),
( 5, 7, 'T', 3, 0 ),
( 6, 6, 'W', 2, 0 );
Recursive CTE:
;WITH cte
AS ( SELECT * ,
ROW_NUMBER() OVER ( ORDER BY t1.[Col 1] ) GroupNo
FROM #Table1 t1
WHERE t1.[Col 1] NOT IN ( SELECT [Col 4] FROM #Table1 )
UNION ALL
SELECT t.* ,
cte.GroupNo
FROM #Table1 t
INNER JOIN cte ON cte.[Col 4] = t.[Col 1]
)
SELECT *
FROM cte
ORDER BY cte.GroupNo , cte.[Row no]
DROP TABLE #Table1
This combines 2 queries with a UNION ALL. The first query finds the top level items where the value of [Col 1] does not appear in [Col 4]:
WHERE t1.[Col 1] NOT IN ( SELECT [Col 4] FROM #Table1 )
The second query finds the child records on the first query with this JOIN:
INNER JOIN cte ON cte.[Col 4] = t.[Col 1]
For the ordering, I've used the following to give the the results of the first query a GroupNo, which is used later to order the records:
ROW_NUMBER() OVER ( ORDER BY t1.[Col 1] ) GroupNo