Recursive query to speed up system - sql

Question

My application reads a table with parent child relation. The application queries every level of the tree on his own and it really slow (must do multiple levels deep). I has searching for another solution and came to the recursive queries. With the examples that I have found I cannot map it to my data structure.
My structure looks like:
CREATE TABLE [products].[BillOfMaterial](
[id] [bigint] IDENTITY(1,1) NOT NULL,
[parentNumber] [nvarchar](50) NOT NULL,
[warehouse] [nvarchar](50) NOT NULL,
[sequenceNumber] [int] NOT NULL,
[childNumber] [nvarchar](50) NOT NULL,
[childDescription] [nvarchar](50) NULL,
[qtyRequired] [numeric](18, 3) NOT NULL,
[childItemClass] [nvarchar](50) NULL,
[childItemType] [nvarchar](50) NULL,
[scrapFactor] [numeric](18, 3) NULL,
[bubbleNumber] [int] NOT NULL,
[operationNumber] [int] NOT NULL,
[effectivityDate] [date] NULL,
[discontinuityDate] [date] NULL,
[companyID] [bigint] NOT NULL,
CONSTRAINT [PK_BillOfMaterial] PRIMARY KEY CLUSTERED
(
[id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
Some example data:
When I query for parentNumber 1 it should give me all those rows:
And for parentNumber 3 the output must be:
Now I need all the children of a parent in a recursive way. How can I achieve this using only sql? (I'm using SQL server)
I tried already using the with statement in sql, but it will now give a lot of results.
WITH bom ( [id]
,[parentNumber]
,[warehouse]
,[sequenceNumber]
,[childNumber]
,[childDescription]
,[qtyRequired]
,[childItemClass]
,[childItemType]
,[scrapFactor]
,[bubbleNumber]
,[operationNumber]
,[effectivityDate]
,[discontinuityDate]
,[companyID] )
AS
(
select * from [CR_ApplicationSuite].[products].[BillOfMaterial] where parentNumber IN ('F611882261', '2912435206')
UNION ALL
select b.* from [CR_ApplicationSuite].[products].[BillOfMaterial] b
INNER JOIN [CR_ApplicationSuite].[products].[BillOfMaterial] c on c.childNumber = b.parentNumber
)
SELECT *
FROM bom

Answer 1

Here's an example that uses a table variable for demonstration purposes.
For a recursive query you need to use the CTE within itself.
I included a rootParentNumber, so it's more obvious what the base parent was.
The WHERE clauses are commented in the example.
Because you can either put a WHERE clause within the Recursive Query, or at the outer query. The former should be faster.
declare #BillOfMaterial TABLE (
[id] [bigint] IDENTITY(1,1) NOT NULL,
[parentNumber] [nvarchar](50) NOT NULL,
[warehouse] [nvarchar](50) NOT NULL,
[sequenceNumber] [int] NOT NULL,
[childNumber] [nvarchar](50) NOT NULL,
[childDescription] [nvarchar](50) NULL,
[qtyRequired] [numeric](18, 3) NOT NULL,
[childItemClass] [nvarchar](50) NULL,
[childItemType] [nvarchar](50) NULL,
[scrapFactor] [numeric](18, 3) NULL,
[bubbleNumber] [int] NOT NULL,
[operationNumber] [int] NOT NULL,
[effectivityDate] [date] NULL,
[discontinuityDate] [date] NULL,
[companyID] [bigint] NOT NULL
);
insert into #BillOfMaterial (parentNumber, childNumber, warehouse, sequenceNumber, qtyRequired, bubbleNumber, operationNumber, companyID) values
('1','2','WH1',1,0,0,0,1),
('2','4','WH1',2,0,0,0,1),
('3','4','WH1',3,0,0,0,1),
('4','5','WH1',4,0,0,0,1),
('5','0','WH1',5,0,0,0,1);
WITH BOM
AS
(
select parentNumber as rootParentNumber, *
from #BillOfMaterial
--where parentNumber IN ('1','3')
union all
select bom.rootParentNumber, b.*
from BOM
INNER JOIN #BillOfMaterial b
on (BOM.childNumber = b.parentNumber and b.childNumber <> '0')
)
SELECT
[rootParentNumber]
,[parentNumber]
,[childNumber]
,[id]
,[warehouse]
,[sequenceNumber]
,[childDescription]
,[qtyRequired]
,[childItemClass]
,[childItemType]
,[scrapFactor]
,[bubbleNumber]
,[operationNumber]
,[effectivityDate]
,[discontinuityDate]
,[companyID]
FROM BOM
--WHERE rootParentNumber IN ('1','3')
ORDER BY [rootParentNumber], [parentNumber], [childNumber]
;