If you want to do a fulltext search (looking in several fields in any order
you will have to customize your mysql configuration file to allow mysql to search for less than 4 character

Check this link
dev.mysql.com/doc/refman/5.0/en/fulltext-fine-tuning.html

The minimum and maximum lengths of words to be indexed are defined by the ft_min_word_len and ft_max_word_len system variables. (See Section 5.1.4, “Server System Variables”.) The default minimum value is four characters; the default maximum is version dependent. If you change either value, you must rebuild your FULLTEXT indexes. For example, if you want three-character words to be searchable, you can set the ft_min_word_len variable by putting the following lines in an option file:

Good news .

I update the subject to resolved.

Best regards.