SQL Compare varchar variable with another varchar variable

Question

I have a Table name lines which has BillId (int) and LineReference (Varchar(100) as two columns. Each billid has LineReference value. However, value in the LineReference might n

Answer 1

1) On medium or long term I would like to normalize this database in order to avoid such mistakes: storing list of values within string/VARCHAR columns. For example, I would use following many to many table:

CREATE TABLE dbo.BillItem (
    ID INT IDENTITY(1,1) PRIMARY KEY,
    BilldID INT NOT NOT NULL REFERENCES dbo.Bill(BilldID),
    ItemID INT NOT NULL REFERENCES dbo.Item(ItemID),
    UNIQUE (BillID, ItemID) -- Unique constraint created in order to prevent duplicated rows
);

In this case, one bill with two items means I have to insert two rows into dbo.BillItem table.

2) Back to original request: for one time task I would use XML and XQuery thus (this solution ends with a SELECT statement but it's trivial to convert into UPDATE):

DECLARE @iCountRef VARCHAR(100) = '1,2,3'

DECLARE @SourceTable TABLE (
    BillId          INT,
    LineReference   VARCHAR(8000)
)

INSERT @SourceTable (BillId, LineReference)
VALUES
(100, '1,2,'),
(100, '1,2,40,34'),
(100, '1'),
(100, '12')

DECLARE @iCountRefAsXML XML = CONVERT(XML, '' + REPLACE(@iCountRef, ',', '') + '')

SELECT  *, STUFF(z.LineReferenceAsXML.query('
    for $i in (x/y)
        for $j in (a/b)
            where data(($i/text())[1]) eq data(($j/text())[1])
        return concat(",", ($i/text())[1])
').value('.', 'VARCHAR(8000)'), 1, 1, '') AS NewLineReference
FROM (
    SELECT  *, CONVERT(XML, 
        '' + REPLACE(LineReference, ',', '') + '' + 
        '' + REPLACE(@iCountRef, ',', '') + ''
    ) AS LineReferenceAsXML
    FROM    @SourceTable s
) z

Results:

BillId      LineReference  NewLineReference LineReferenceAsXML                                                      
----------- -------------  ---------------- ------------------------------------------------------------------------
100         1,2,           1 ,2             12123             
100         1,2,40,34      1 ,2             124034123
100         1              1                1123                          
100         12             (null)           12123