How to create functions that affect only a specific user

get_currentuserinfo();
if ( $current_user->ID === <ID of user to isolate>) {
   // user specific code
}

http://codex.wordpress.org/Function_Reference/get_currentuserinfo

That is a very general solution. There may be other/better solutions but you didn’t provide much information about what you are trying to accomplish.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)