Search with relevance ranking using containstable and freetext - sql-server-2008

Question

I've read that you can rank the result from a search using containstable along with contains and freetext under SQL 2008 server. I've just recently used freetext for the first time. Free text loops through the words separately and compares to the indexed column. I want to be able to search for phrases first and then single words.
Let's say the description column is indexed. I'm using a stored procedure query like this:
SELECT id, description, item from table where (FREETEXT(description,#strsearch))
Example if 3 rowsets contains words with apples in them and I search for 'apple cake', the row-set with id2 should be first, then the other two should follow:
id1 apple pie 4/01/2012
id2 apple cake 2/29/2011
id3 candy apple 5/9/2011
Example if 4 rowsets contains words with food in them and I search for 'fast food restaurant', the row-set with id3 should be first, followed by id1 (not an exact match but because it has 'fast food' in the column), then the other two should follow:
id1 McDonalds fast food
id2 healthy food
id3 fast food restaurant
id4 Italian restaurant

Answer 1

Does this article help?
MSDN : Limiting Ranked Result Sets (Full-Text Search)
It implies, in part, that using an additional parameter will allow you to limit the result to the ones with the greatest relevance (which you can influence using WEIGHT) and also order by that relevance (RANK).
top_n_by_rank is an integer value, n, that specifies that only the n
highest ranked matches are to be returned, in descending order.
The doc doesn't have an example for FREETEXT; it only references CONTAINSTABLE. But it definitely implies that CONTAINSTABLE outputs a RANK column that you could use to ORDER BY.
I don't know if there is any way to enforce your own definition of relevance. It may make sense to pull out the top 10 relevant matches according to FTS, then apply your own ranking on the output, e.g. you can split up the search terms using a function, and order by how many of the words matched. For simplicity and easy repro in the following example I am not using Full-Text in the subquery but you can replace it with whatever you're actually doing. First create the function:
IF OBJECT_ID('dbo.SplitStrings') IS NOT NULL
DROP FUNCTION dbo.SplitStrings;
GO
CREATE FUNCTION dbo.SplitStrings(#List NVARCHAR(MAX))
RETURNS TABLE
AS
RETURN ( SELECT Item FROM
( SELECT Item = x.i.value('(./text())[1]', 'nvarchar(max)')
FROM ( SELECT [XML] = CONVERT(XML, '<i>'
+ REPLACE(#List, ' ', '</i><i>') + '</i>').query('.')
) AS a CROSS APPLY [XML].nodes('i') AS x(i) ) AS y
WHERE Item IS NOT NULL
);
GO
Then a simple script that shows how to perform the matching:
DECLARE #foo TABLE
(
id INT,
[description] NVARCHAR(450)
);
INSERT #foo VALUES
(1,N'McDonalds fast food'),
(2,N'healthy food'),
(3,N'fast food restaurant'),
(4,N'Italian restaurant'),
(5,N'Spike''s Junkyard Dogs');
DECLARE #searchstring NVARCHAR(255) = N'fast food restaurant';
SELECT x.id, x.[description]--, MatchCount = COUNT(s.Item)
FROM
(
SELECT f.id, f.[description]
FROM #foo AS f
-- pretend this actually does full-text search:
--where (FREETEXT(description,#strsearch))
-- and ignore how I actually matched:
INNER JOIN dbo.SplitStrings(#searchstring) AS s
ON CHARINDEX(s.Item, f.[description]) > 0
GROUP BY f.id, f.[description]
) AS x
INNER JOIN dbo.SplitStrings(#searchstring) AS s
ON CHARINDEX(s.Item, x.[description]) > 0
GROUP BY x.id, x.[description]
ORDER BY COUNT(s.Item) DESC, [description];
Results:
id description
-- -----------
3 fast food restaurant
1 McDonalds fast food
2 healthy food
4 Italian restaurant