Improving my user class
In short : its an extremely bad piece of code.

Here is a list or "whys":


you are mixing data access with logic ( sql queries should be handled by different object )
you are using global state for DB access 
there is some mystical parameter $full in full_name() method
all the methods are getters
the SQL queries happen each time you use a getter
parameter $id means nothing ( is it a string , a number , some other object ? )


Basically what you have there are five standalone procedures wrapped up in an a class just for show.