Simplest way to do a recursive self-join? - sql

Question

What is the simplest way of doing a recursive self-join in SQL Server? I have a table like this:
PersonID | Initials | ParentID
1 CJ NULL
2 EB 1
3 MB 1
4 SW 2
5 YT NULL
6 IS 5
And I want to be able to get the records only related to a hierarchy starting with a specific person. So If I requested CJ's hierarchy by PersonID=1 I would get:
PersonID | Initials | ParentID
1 CJ NULL
2 EB 1
3 MB 1
4 SW 2
And for EB's I'd get:
PersonID | Initials | ParentID
2 EB 1
4 SW 2
I'm a bit stuck on this can can't think how to do it apart from a fixed-depth response based on a bunch of joins. This would do as it happens because we won't have many levels but I would like to do it properly.
Thanks! Chris.

Answer 1

WITH q AS
(
SELECT *
FROM mytable
WHERE ParentID IS NULL -- this condition defines the ultimate ancestors in your chain, change it as appropriate
UNION ALL
SELECT m.*
FROM mytable m
JOIN q
ON m.parentID = q.PersonID
)
SELECT *
FROM q
By adding the ordering condition, you can preserve the tree order:
WITH q AS
(
SELECT m.*, CAST(ROW_NUMBER() OVER (ORDER BY m.PersonId) AS VARCHAR(MAX)) COLLATE Latin1_General_BIN AS bc
FROM mytable m
WHERE ParentID IS NULL
UNION ALL
SELECT m.*, q.bc + '.' + CAST(ROW_NUMBER() OVER (PARTITION BY m.ParentID ORDER BY m.PersonID) AS VARCHAR(MAX)) COLLATE Latin1_General_BIN
FROM mytable m
JOIN q
ON m.parentID = q.PersonID
)
SELECT *
FROM q
ORDER BY
bc
By changing the ORDER BY condition you can change the ordering of the siblings.

Answer 2

Using CTEs you can do it this way
DECLARE #Table TABLE(
PersonID INT,
Initials VARCHAR(20),
ParentID INT
)
INSERT INTO #Table SELECT 1,'CJ',NULL
INSERT INTO #Table SELECT 2,'EB',1
INSERT INTO #Table SELECT 3,'MB',1
INSERT INTO #Table SELECT 4,'SW',2
INSERT INTO #Table SELECT 5,'YT',NULL
INSERT INTO #Table SELECT 6,'IS',5
DECLARE #PersonID INT
SELECT #PersonID = 1
;WITH Selects AS (
SELECT *
FROM #Table
WHERE PersonID = #PersonID
UNION ALL
SELECT t.*
FROM #Table t INNER JOIN
Selects s ON t.ParentID = s.PersonID
)
SELECT *
FROm Selects

Answer 3

The Quassnoi query with a change for large table. Parents with more childs then 10: Formating as str(5) the row_number()
WITH q AS
(
SELECT m.*, CAST(str(ROW_NUMBER() OVER (ORDER BY m.ordernum),5) AS VARCHAR(MAX)) COLLATE Latin1_General_BIN AS bc
FROM #t m
WHERE ParentID =0
UNION ALL
SELECT m.*, q.bc + '.' + str(ROW_NUMBER() OVER (PARTITION BY m.ParentID ORDER BY m.ordernum),5) COLLATE Latin1_General_BIN
FROM #t m
JOIN q
ON m.parentID = q.DBID
)
SELECT *
FROM q
ORDER BY
bc

Answer 4

SQL 2005 or later, CTEs are the standard way to go as per the examples shown.
SQL 2000, you can do it using UDFs -
CREATE FUNCTION udfPersonAndChildren
(
#PersonID int
)
RETURNS #t TABLE (personid int, initials nchar(10), parentid int null)
AS
begin
insert into #t
select * from people p
where personID=#PersonID
while ##rowcount > 0
begin
insert into #t
select p.*
from people p
inner join #t o on p.parentid=o.personid
left join #t o2 on p.personid=o2.personid
where o2.personid is null
end
return
end
(which will work in 2005, it's just not the standard way of doing it. That said, if you find that the easier way to work, run with it)
If you really need to do this in SQL7, you can do roughly the above in a sproc but couldn't select from it - SQL7 doesn't support UDFs.

Answer 5

Check following to help the understand the concept of CTE recursion
DECLARE
#startDate DATETIME,
#endDate DATETIME
SET #startDate = '11/10/2011'
SET #endDate = '03/25/2012'
; WITH CTE AS (
SELECT
YEAR(#startDate) AS 'yr',
MONTH(#startDate) AS 'mm',
DATENAME(mm, #startDate) AS 'mon',
DATEPART(d,#startDate) AS 'dd',
#startDate 'new_date'
UNION ALL
SELECT
YEAR(new_date) AS 'yr',
MONTH(new_date) AS 'mm',
DATENAME(mm, new_date) AS 'mon',
DATEPART(d,#startDate) AS 'dd',
DATEADD(d,1,new_date) 'new_date'
FROM CTE
WHERE new_date < #endDate
)
SELECT yr AS 'Year', mon AS 'Month', count(dd) AS 'Days'
FROM CTE
GROUP BY mon, yr, mm
ORDER BY yr, mm
OPTION (MAXRECURSION 1000)

Answer 6

DELIMITER $$
DROP PROCEDURE IF EXISTS `myprocDURENAME`$$
CREATE DEFINER=`root`#`%` PROCEDURE `myprocDURENAME`( IN grp_id VARCHAR(300))
BEGIN
SELECT h.ID AS state_id,UPPER(CONCAT( `ACCNAME`,' [',b.`GRPNAME`,']')) AS state_name,h.ISACTIVE FROM accgroup b JOIN (SELECT get_group_chield (grp_id) a) s ON FIND_IN_SET(b.ID,s.a) LEFT OUTER JOIN acc_head h ON b.ID=h.GRPID WHERE h.ID IS NOT NULL AND H.ISACTIVE=1;
END$$
DELIMITER ;
////////////////////////
DELIMITER $$
DROP FUNCTION IF EXISTS `get_group_chield`$$
CREATE DEFINER=`root`#`%` FUNCTION `get_group_chield`(get_id VARCHAR(999)) RETURNS VARCHAR(9999) CHARSET utf8
BEGIN
DECLARE idd VARCHAR(300);
DECLARE get_val VARCHAR(300);
DECLARE get_count INT;
SET idd=get_id;
SELECT GROUP_CONCAT(id)AS t,COUNT(*) t1 INTO get_val,get_count FROM accgroup ag JOIN (SELECT idd AS n1) d ON FIND_IN_SET(ag.PRNTID,d.n1);
SELECT COUNT(*) INTO get_count FROM accgroup WHERE PRNTID IN (idd);
WHILE get_count >0 DO
SET idd=CONCAT(idd,',', get_val);
SELECT GROUP_CONCAT(CONCAT('', id ,'' ))AS t,COUNT(*) t1 INTO get_val,get_count FROM accgroup ag JOIN (SELECT get_val AS n1) d ON FIND_IN_SET(ag.PRNTID,d.n1);
END WHILE;
RETURN idd;
-- SELECT id FROM acc_head WHERE GRPID IN (idd);
END$$
DELIMITER ;