SQL Server 2008 update table and switch values query optimization - sql-server

Question

I have a table with values
ID Son Father
----------- ---------- ----------
1 Mark Gerard
2 Gerard Ivan
3 Leo Samuel
4 Samuel Johan
5 Ivan Carles
I need to change table like this:
ID Son Father
----------- ---------- ----------
1 Mark Carles
2 Gerard Carles
3 Leo Johan
4 Samuel Johan
5 Ivan Carles
The goal is to find a major 'Father' and update all 'Son' records with this value. Major 'Father' can be different.
My code is next:
DECLARE #CNT INT
DECLARE #CH_1 NVARCHAR(10)
DECLARE #CH_2 NVARCHAR(10)
CREATE TABLE #PPL (ID INT, Son NVARCHAR(10), Father NVARCHAR(10))
INSERT INTO #PPL VALUES (1, 'Mark', 'Gerard')
INSERT INTO #PPL VALUES (2, 'Gerard', 'Ivan')
INSERT INTO #PPL VALUES (3, 'Leo', 'Samuel')
INSERT INTO #PPL VALUES (4, 'Samuel', 'Johan')
INSERT INTO #PPL VALUES (5, 'Ivan', 'Carles')
SET #I = 1
SET #CNT = (SELECT COUNT(ID) FROM #PPL)
WHILE #I <= #CNT
BEGIN
SET #J = 1
WHILE #J <= #CNT
BEGIN
SET #CH_1 = (SELECT Son FROM #PPL WHERE ID = #J)
SET #CH_2 = (SELECT Father FROM #PPL WHERE ID = #J)
UPDATE #PPL SET Father = #CH_2 WHERE Father = #CH_1
SET #J = #J + 1
END;
SET #I = #I + 1
END;
SELECT * FROM #PPL
DROP TABLE #PPL
This code is working correct, but for the low number of records. How this code can be optimized?
Thanks!

Answer 1

Here is how you can do it with a recursive CTE.
CREATE TABLE #PPL (ID INT, Son NVARCHAR(10), Father NVARCHAR(10))
INSERT INTO #PPL VALUES (1, 'Mark', 'Gerard')
INSERT INTO #PPL VALUES (2, 'Gerard', 'Ivan')
INSERT INTO #PPL VALUES (3, 'Leo', 'Samuel')
INSERT INTO #PPL VALUES (4, 'Samuel', 'Johan')
INSERT INTO #PPL VALUES (5, 'Ivan', 'Carles')
;WITH CTE_FamilyGenealogy
AS
(
SELECT ID
,Son
,Father
,1 AS [Level]
FROM #PPL Ancor
UNION ALL
SELECT CTE_FamilyGenealogy.ID
,CTE_FamilyGenealogy.Son
,Fathers.Father AS Father
,CTE_FamilyGenealogy.[Level] + 1 AS [Level]
FROM #PPL Fathers
INNER JOIN CTE_FamilyGenealogy ON CTE_FamilyGenealogy.Father = Fathers.Son
),
CTE_MajorFathers
AS
(
SELECT ID
,Son
,Father
,ROW_NUMBER() OVER (PARTITION BY Son ORDER BY [Level] DESC) AS RowRank
FROM CTE_FamilyGenealogy
)
SELECT ID
,Son
,Father
FROM CTE_MajorFathers
WHERE RowRank = 1
ORDER BY ID
The Recursive CTE CTE_FamilyGenealogy finds all the father son combination and determine the level within the family tree. The CTE_MajorFathers
CTE uses ROW_NUMBER to rank the possible combinations based on the Level with in the FamilyGenealogy to determine the Major Father.

Answer 2

Try following approach base on recursion (see recursive Common Table Expressions) and HIERARCHYID (SQL2008+) data type. The basic idea is to build for every row one hierarchy value starting from the "first" father :-) and ending with "last" son :-). For example: for first row (1, 'Mark', 'Gerard') this node/family tree is /5/2/1/ where /5/ is "first" father ;-) and /1/ is the "last" son. Next it convert these values to hiearchyid values and it uses GetLevel and GetAncestor methods to compute the "first" father: Father1ID: Johan or Carles.
IF OBJECT_ID('tempdb.dbo.#Results') IS NOT NULL
BEGIN
DROP TABLE #Results;
END
CREATE TABLE #Results (ID INT NOT NULL PRIMARY KEY, Father1ID INT);
WITH CteRec
AS (
-- It returns Father only rows
SELECT l1.ID, l1.Son, l1.Father, CONVERT(VARCHAR(900), '/'+LTRIM(l1.ID)+'/') AS Node -- FamilyTree
FROM #PPL AS l1 -- First level
WHERE NOT EXISTS(SELECT * FROM #PPL p WHERE p.Son = l1.Father)
UNION ALL
-- It returns Son only and Son-Father rows
SELECT ln.ID, ln.Son, ln.Father, CONVERT(VARCHAR(900), prt.Node+LTRIM(ln.ID)+'/') AS Node -- FamilyTree
FROM #PPL AS ln -- Next level
JOIN CteRec AS prt ON prt.Son = ln.Father
)
INSERT #Results (ID, Father1ID)
SELECT ID,
Father1ID = CONVERT(INT,REPLACE(CONVERT(HIERARCHYID, Node).GetAncestor(CONVERT(HIERARCHYID, Node).GetLevel()-1).ToString(),'/',''))
FROM CteRec;
SELECT p.*, r.Father1ID, rp.Father AS Father1Name
FROM #PPL p
INNER JOIN #Results r ON p.ID = r.ID
INNER JOIN #PPL rp ON r.Father1ID = rp.ID
-- Also you ca use #Result with UPDATE statement but I would store this values within new column Father1

Answer 3

Recursive CTE's are overrated =)
This simple approach will run through just as fast (on normal data), will never complain about max recursion and is easy to read. The only downside I can see is that it might go into an eternal loop when the data is corrupt.
CREATE TABLE #PPL (ID INT, Son NVARCHAR(10), Father NVARCHAR(10))
INSERT INTO #PPL VALUES (1, 'Mark', 'Gerard')
INSERT INTO #PPL VALUES (2, 'Gerard', 'Ivan')
INSERT INTO #PPL VALUES (3, 'Leo', 'Samuel')
INSERT INTO #PPL VALUES (4, 'Samuel', 'Johan')
INSERT INTO #PPL VALUES (5, 'Ivan', 'Carles')
DECLARE #rowcount int = -1
WHILE #rowcount <> 0
BEGIN
UPDATE upd
SET Father = new.Father
FROM #PPL upd
JOIN #PPL new
ON new.Son = upd.Father
WHERE upd.Father <> new.Father
SELECT #rowcount = ##ROWCOUNT
END
SELECT * FROM #PPL
PS: it probably helps to have an index on the Son column when running on large datasets.