Very slow queries with custom MySQL function

[glictevo]

Hello,

I am currently developping a module which acts as a search engine for data I have in the database.
 

I retrieve data from the searched words by doing a query like this for each word : SELECT id, levenshtein_ratio("' . pQSL($word) . '", column_name) AS lev FROM ' . _DB_PREFIX . 'my_table
The table has 50 000 entries.
The levenshtein_ratio is a function I added in the database directly.

The thing is that when I run the query from my controller, it takes 11 seconds, but running from phpMyAdmin it takes on average 0.005 seconds.

I have several columns on which I would like to call the levenshtein_ratio function, but each time I use it it take 12 more seconds on average.

Does anyone have an idea on why it is so slow ?

Thanks