Parent and Child Recursion Logic in SQL Server

Question

I need some help with the following code.

DECLARE @BomStructure TABLE
                      (
                          ParentPart Varchar(50), 
                          Component Varchar(50)
                      )  -- Parent & Child

INSERT @BomStructure VALUES ('P01-1000W', 'P01-1000WX');
INSERT @BomStructure VALUES ('P01-1000W', 'PKG-INSERT1000' );
INSERT @BomStructure VALUES ('P01-1000W', 'PKG-HANG CARD-XL' );
INSERT @BomStructure VALUES ('P01-1000W', 'PKG-BAG10' );
INSERT @BomStructure VALUES ('P01-1000W', 'PKG-BAG16');
INSERT @BomStructure VALUES ('P01-1000W', 'BOX RSC-01');
INSERT @BomStructure VALUES ('P01-1000W', 'F92-0306');
INSERT @BomStructure VALUES ('P01-1000WX', 'P01-1000W-TOP');
INSERT @BomStructure VALUES ('P01-1000WX', 'P01-1000W-BACK');
INSERT @BomStructure VALUES ('P01-1000WX', 'P01-1000W-BOTTOM');
INSERT @BomStructure VALUES ('P01-1000W-TOP', 'P12-5060WHA96');
INSERT @BomStructure VALUES ('P01-1000W-BACK', 'P12-5060WHA96');
INSERT @BomStructure VALUES ('P01-1000W-BOTTOM', 'P12-5060WHA96');
INSERT @BomStructure VALUES('PKG-INSERT1000', 'LABOR-KIT');

;WITH Relation AS 
(
    SELECT 
        ParentPart, Component, 
        0 AS Level,
        CAST(Component AS VARCHAR(255)) AS Path
    FROM 
        @BomStructure 

    UNION ALL

    SELECT 
        i.ParentPart, i.Component,
        Level + 1,
        CAST(Path + '/' + CAST(i.Component AS VARCHAR(255)) AS VARCHAR(255)) AS Path
    FROM 
        @BomStructure i 
    INNER JOIN 
        Relation RL ON RL.ParentPart = i.Component
)
SELECT * 
FROM Relation 
WHERE ParentPart = 'P01-1000W' 
ORDER BY Level, Component

The output that I'm getting with this:

ParentPart  Component   Level   Path
--------------------------------------------
P01-1000W   BOX RSC-01  0   BOX RSC-01
P01-1000W   F92-0306    0   F92-0306
P01-1000W   P01-1000WX  0   P01-1000WX
P01-1000W   PKG-BAG10   0   PKG-BAG10
P01-1000W   PKG-BAG16   0   PKG-BAG16
P01-1000W   PKG-HANG CARD-XL    0   PKG-HANG CARD-XL
P01-1000W   PKG-INSERT1000  0   PKG-INSERT1000
P01-1000W   P01-1000WX  1   P01-1000W-BOTTOM/P01-1000WX
P01-1000W   P01-1000WX  1   P01-1000W-BACK/P01-1000WX
P01-1000W   P01-1000WX  1   P01-1000W-TOP/P01-1000WX
P01-1000W   PKG-INSERT1000  1   LABOR-KIT/PKG-INSERT1000
P01-1000W   P01-1000WX  2   P12-5060WHA96/P01-1000W-BOTTOM/P01-1000WX
P01-1000W   P01-1000WX  2   P12-5060WHA96/P01-1000W-BACK/P01-1000WX
P01-1000W   P01-1000WX  2   P12-5060WHA96/P01-1000W-TOP/P01-1000WX

For any ParentPart that has level 2 or greater structure, I want to see the path's immediate parent

See below desired output for example

Really appreciate your help. Thanks!

Answer 1

Just don't build the path and instead store the component you start with

 ;WITH Relation AS (
  SELECT ParentPart, Component
  , 0 AS Level
  ,Component as start_component 
  FROM @BomStructure 
  UNION ALL
  SELECT i.ParentPart, i.Component
  , Level + 1
  ,RL.start_Component
  FROM @BomStructure i 
  INNER JOIN Relation RL ON RL.ParentPart = i.Component)