The key to manipulating the rankings is to use a union. For each column you use a separate select statement. In that statement, add an identifier that shows from which column each row was pulled then. Insert the results into a table variable, then you can manipulate the ranking by sorting on the identifier or multiplying the rank by some value based on the identifier.
The key is to give the appearance of modifying the ranking, not to actually change sql server's ranking.
Example using a table variable:
DECLARE @Results TABLE (PersonId Int, Rank Int, Source Int)
For table People with Columns PersonId Int PK Identity, FirstName VarChar(100), MiddleName VarChar(100), LastName VarChar(100), AlsoKnown VarChar(100) with each column added to a full text catalog, you could use the query:
INSERT INTO @Results (PersonId, Rank, Source)
SELECT PersonId, Rank, 1
FROM ContainsTable(People, FirstName, @SearchValue) CT INNER JOIN People P ON CT.Key = P.PersonId
UNION
SELECT PersonId, Rank, 2
FROM ContainsTable(People, MiddleName, @SearchValue) CT INNER JOIN People P ON CT.Key = P.PersonId
UNION
SELECT PersonId, Rank, 3
FROM ContainsTable(People, LastName, @SearchValue) CT INNER JOIN People P ON CT.Key = P.PersonId
UNION
SELECT PersonId, Rank, 4
FROM ContainsTable(People, AlsoKnown, @SearchValue) CT INNER JOIN People P ON CT.Key = P.PersonId
/*
Now that the results from above are in the @Results table, you can manipulate the
rankings in one of several ways, the simplest is to pull the results ordered first by Source then by Rank. Of course you would probably join to the People table to pull the name fields.
*/
SELECT PersonId
FROM @Results
ORDER BY Source, Rank DESC
/*
A more complex manipulation would use a statement to multiply the ranking by a value above 1 (to increase rank) or less than 1 (to lower rank), then return results based on the new rank. This provides more fine tuning, since I could make first name 10% higher and middle name 15% lower and leave last name and also known the original value.
*/
SELECT PersonId, CASE Source WHEN 1 THEN Rank * 1.1 WHEN 2 THEN Rank * .9 ELSE Rank END AS NewRank FROM @Results
ORDER BY NewRank DESC
The one downside is you'll notice I didn't use UNION ALL, so if a word appears in more than one column, the rank won't reflect that. If that's an issue you could use UNION ALL and then remove duplicate person id's by adding all or part of the duplicate record's rank to the rank of another record with the same person id.