I'm building a category list and I'm unsure how to store the Ampersand symbol
in MySQL database. Is there any problem/disadvantage if I use '&'. Are there any differences
from using it in a html format '&'?
Using '&' saves a few bytes. It is not a special character for MySQL. You can easily produce the & for output later with PHP's method htmlspecialchars(). When your field is meant to keep simple information, you should use plain text only, as this is in general more flexible since you can generate different kinds of markup etc. later. Exception: the markup is produced by a user whose layout decisions you want to save with the text (as in rich-text input). If you have tags etc. in your input, you may want to use & for consistency.