According to the MySQL manual
Full-text indexes can be used only with MyISAM tables
I’m using an InnoDB table-type however, so had to look at other ways of implementing a full-text search that would give me rankings by relevance, to order the results by.
It’s possible to do the ranking with PHP, by doing a
LIKE '%term%' MySQL query and then doing a substring count for each search term, but I believe that doing it via MySQL would be faster, and way cooler.