Flatten association table to multi-value column?

Question

I have a table with just product ID\'s and category ID\'s (products can be in more than one category). How can I flatten the category ID\'s into a product column so I end us

Answer 1

Use a function.
This does a lookup to text so you will need to adapt.
The COALESCE is just to put a ,.
This is from a large scale production application - it works and it fast.
Function was questioned by JustinPony as function is slow
I am hitting some tables of million of records but only returning 100 rows.
The function is only applied to the hundred rows.

usage:

select top 5 sID, ( select [dbo].[JoinMVEnum](docSVsys.sID, '140') ) as [Flag Issue]
from docSVsys

function

SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE FUNCTION [dbo].[JoinMVText]
(
   @sID int,
   @fieldID tinyint
)
RETURNS VARCHAR(MAX)
AS 
BEGIN
    DECLARE @MVtextList varchar(max)
    SELECT @MVtextList = COALESCE(@MVtextList + '; ', '') + docMVtext.value
    FROM docMVtext with (nolock) 
    WHERE docMVtext.sID = @sID and fieldID = @fieldID
    RETURN @MVtextList
END

GO