Problem using LIKE with FORCE INDEX...

[Jonathan Segura Castro]

Hi.. I have a question, because when I try to use the LIKE sentence with the FORCE INDEX sentence, the LIKE sentence ignore it.?? I have the next SQL

EXPLAIN SELECT filename FROM users u force index (uniqUsername) where username like "%ill%" ;

The result is:

possible_keys = NULL
key = NULL

Where that table has a index named "uniqUsername" ??..
Why the LIKE sentence not repect it?

Thank's