MySQL by default requires minimum of 4 alphabets to perform a search.

Here is a way to modify the minimum number on CentOS:

# mysql -u root

# nano /etc/my.cnf

add the below line and save it, the number indicate the minimum length for the search, here we put 3.

ft_min_word_len=3

# service mysqld restart

rebuild the fulltext index of sql and it should work.