I want to make one column more valuable than others like it's been done in query bellow.[This example ][1] shows that only one fulltext index is needed And [this answer][2]suggests that three fulltext indexes are needed to do the same. 

Here is the queries from the first link:

    ALTER TABLE products ADD FULLTEXT(title, sdescription, ldescription)

    SELECT *,
    MATCH(`title`) AGAINST ('+iphone +case +4s' IN BOOLEAN MODE) * 10 as rel1,
    MATCH(`sdescription`) AGAINST ('+iphone +case +4s' IN BOOLEAN MODE) * 3 as rel2,
    MATCH(`ldescription`) AGAINST ('+iphone +case +4s' IN BOOLEAN MODE) as rel3,
    FROM products
    WHERE MATCH (title, sdescription, ldescription) 
      AGAINST ('+iphone +case +4s' IN BOOLEAN MODE)
    ORDER BY (rel1)+(rel2)+(rel3) DESC;

I'm confused how many indexes are needed for that, one or three?
I asked this question on stackoverflow but not answer yet.

  [1]: http://www.vionblog.com/mysql-full-text-search-with-multiple-words/
  [2]: http://stackoverflow.com/questions/547542/how-can-i-manipulate-mysql-fulltext-search-relevance-to-make-one-field-more-val/600915#600915