SQL Server Recursive Query to get Top parent - sql

Question

I need your help on making on recursive query using a CTE in SQL Server.
I have order no as input parameter.. I need to display its top parent despatch details. even if I search for its children.. ie if I search for order no 3 I should get its top parent order no. that is 20.
Here is my table structure..
CREATE TABLE #TblSerialNo
(
[SRno] [char](20) NOT NULL ,
[CustSrNo] [varchar](75) NULL
)
CREATE TABLE #TblSerialReleation
(
[SRno] [char](20) NOT NULL ,
[ChildSRno] [char](20) NOT NULL
)
CREATE TABLE #TblDespatch
(
[SRno] [char](20) NOT NULL ,
OrderNo INT NOT NULL
)
INSERT INTO #TblSerialNo VALUES ( 'TS1', 'DD123CV1' )
INSERT INTO #TblSerialNo VALUES ( 'TS2', 'DD123CV2' )
INSERT INTO #TblSerialNo VALUES ( 'TS3', 'DD123CV3' )
INSERT INTO #TblSerialNo VALUES ( 'BS1', 'DD12sfs3CV1' )
INSERT INTO #TblSerialNo VALUES ( 'BS2', 'DD1et23CV2' )
INSERT INTO #TblSerialNo VALUES ( 'CS1', 'DD12e3CV1' )
INSERT INTO #TblSerialNo VALUES ( 'CS2', 'DD12fe3CV2' )
INSERT INTO #TblSerialNo VALUES ( 'BS1aa', 'DD12d3CV1' )
INSERT INTO #TblSerialNo VALUES ( 'BS1ab', 'DDd123CV2' )
INSERT INTO #TblSerialNo VALUES ( 'BS1ac', 'DD1r23CV3' )
INSERT INTO #TblSerialNo VALUES ( 'BS2aa', 'DDs123CV4' )
INSERT INTO #TblSerialNo VALUES ( 'BS2ab', 'DD12d3CV1' )
INSERT INTO #TblSerialNo VALUES ( 'BS2ac', 'DD1s23CV2' )
INSERT INTO #TblSerialNo VALUES ( 'CS1aa', 'DD1s23CV3' )
INSERT INTO #TblSerialNo VALUES ( 'CS1ab', 'DD12s3CV4' )
INSERT INTO #TblSerialNo VALUES ( 'CS1ac', 'DD123dCV1' )
INSERT INTO #TblSerialNo VALUES ( 'CS2aa', 'DDa123CV2' )
INSERT INTO #TblSerialNo VALUES ( 'CS2ab', 'DDa123CV3' )
INSERT INTO #TblSerialNo VALUES ( 'CS2ac', 'DDa123CV4' )
--================ Relation table ==============
INSERT INTO #TblSerialReleation VALUES ( 'TS1', 'BS1' )
INSERT INTO #TblSerialReleation VALUES ( 'TS1', 'BS2' )
INSERT INTO #TblSerialReleation VALUES ( 'TS2', 'CS1' )
INSERT INTO #TblSerialReleation VALUES ( 'TS2', 'CS2' )
INSERT INTO #TblSerialReleation VALUES ( 'BS1', 'BS1aa' )
INSERT INTO #TblSerialReleation VALUES ( 'BS1', 'BS1ab' )
INSERT INTO #TblSerialReleation VALUES ( 'BS1', 'BS1ac' )
INSERT INTO #TblSerialReleation VALUES ( 'BS2', 'BS2aa' )
INSERT INTO #TblSerialReleation VALUES ( 'BS2', 'BS2ab' )
INSERT INTO #TblSerialReleation VALUES ( 'BS2', 'BS2ac' )
INSERT INTO #TblSerialReleation VALUES ( 'CS1', 'CS1aa' )
INSERT INTO #TblSerialReleation VALUES ( 'CS1', 'CS1ab' )
INSERT INTO #TblSerialReleation VALUES ( 'CS1', 'CS1ac' )
INSERT INTO #TblSerialReleation VALUES ( 'CS2', 'CS2aa' )
INSERT INTO #TblSerialReleation VALUES ( 'CS2', 'CS2ab' )
INSERT INTO #TblSerialReleation VALUES ( 'CS2', 'CS2ac' )
--=========== Despatch
INSERT INTO #TblDespatch VALUES ( 'CS2ac', 1 )
INSERT INTO #TblDespatch VALUES ( 'CS2ab', 1 )
INSERT INTO #TblDespatch VALUES ( 'CS2ac', 1 )
INSERT INTO #TblDespatch VALUES ( 'CS1aa', 1 )
INSERT INTO #TblDespatch VALUES ( 'CS1ac', 1 )
INSERT INTO #TblDespatch VALUES ( 'CS2ac', 1 )
INSERT INTO #TblDespatch VALUES ( 'CS2ac', 1 )
INSERT INTO #TblDespatch VALUES ( 'TS1', 1 )
INSERT INTO #TblDespatch VALUES ( 'TS3', 2 )
INSERT INTO #TblDespatch VALUES ( 'TS2', 3 )
INSERT INTO #TblDespatch VALUES ( 'BS2ab', 20 )
DROP TABLE #TblDespatch
DROP TABLE #TblSerialNo
DROP TABLE #TblSerialReleation
Thanks in advance.

Answer 1

Looking at your data, the relation seems to go the other way around (BS2ab (Order 20) is the child of TS1(Order 3) through BS2.
If this is the case, starting from the child (BS2ab) you can find its top parent with the following statement:
;with ParentOrders as(
select
convert(char(20), 'BS2ab')as SRno,
0 as Level
union all
select r.SRno, o.Level + 1
from ParentOrders o
join TblSerialReleation r
on o.SRNo = r.ChildSRno
)
select top 1 SRNO
from ParentOrders
order by Level desc
Here's a working sample of the query: http://www.sqlfiddle.com/#!3/e253e/6