simplest way to do recursive t-sql for multiple selects - tsql

Question

I am developing a Bill Of Materials cost calculator program and I am struggling to fathom a simple solution to some recursive selects I want.
I am using SQL Server 2005 for this part of the application.
Say I have Product A, which contains assembly B, and Part C. Assembly B will contain parts D and E, but, here is where I struggle, D and or E may contain X number of other assemblies.
I can do something along the lines of;
SELECT * FROM TBLBOM WHERE Parent = A
UNION
SELECT * FROM TBLBOM WHERE Parent = B
UNION
SELECT * FROM TBLBOM WHERE Parent = C
To produce something along the lines of;
PARENT COMP COST
A X £1
B D £0.5
B E £0.5
....
C Y £1
But lets say Component D is made up of Component F & G, how would I accommodate this in a t-sql statement.
In a nutshell, I need to expand out the full component list of all assemblies that are associated to a parent product regardless of whether they are in a sub assembly or a sub assembly of a sub assembly etc...
Ideally I would like to avoid a cursor at all costs :)
Any help / guidance would be appreciated.
Thank you.
EDIT;
As requested, here is the table structure and expected output. The parent is the DRAWINGNO and the child node is the PART (which could also be a parent in itself);
BOMID DRAWINGNO ITEM PART COST
1303 HGR05180 1 HGR05370 1
1304 HGR05180 2 HGF65050 4
1305 HGR05180 3 HGF50340 1
1312 HGR05370 1 HPN05075 1
1313 HGR05370 2 HPN05085 2
1314 HGR05370 3 HPN05080 1
1848 EXP-18G 1 HGR05180 1
1849 EXP-18G 2 HGR05210 3
1850 EXP-18G 3 HGR05230 1
1851 EXP-18G 4 HGR05140 1
1852 EXP-18G 5 HGR05150 2
1853 EXP-18G 6 HGR05050 1
1854 EXP-18G 7 ESC05350 1
1855 EXP-18G 8 ESC05330 3
1856 EXP-18G 9 HGR05360 1
1857 EXP-18G 10 HGR05370 2
1858 EXP-18G 11 ESC05640 1

Answer 1

If i understand (and without table structure) you can try something like this
DECLARE #Table TABLE(
Component VARCHAR(50),
Parent VARCHAR(50),
Cost FLOAT
)
INSERT INTO #Table SELECT 'B', 'A', 1
INSERT INTO #Table SELECT 'C', 'B', 2
INSERT INTO #Table SELECT 'C', 'B', 3
INSERT INTO #Table SELECT 'D', 'C', 4
DECLARE #Product VARCHAR(50)
SET #Product = 'A'
;WITH Selects AS (
SELECT *
FROM #Table
WHERE Parent = #Product
UNION ALL
SELECT t.*
FROM #Table t INNER JOIN
Selects s ON t.Parent = s.Component
)
SELECt *
FROm Selects

Answer 2

You want to be using recursive common table expression (CTEs). Books Online has a lot of information on how to use these; in the index, look up CTEs and pick the "Recursive Queries Using Common Table Expressions" entry. (I've had problems before linking to BOL online, or I'd try to link it here.)
Also, if you post your table structure, you should get half a dozen examples within five minutes. Better yet, try and search SO for prior examples.