Quando la variabile non e' impostata vuole dire che il while non viene eseguito perche' evidentemente nessuna riga della tabella soddisfa la SELECT.
Il messaggio che ti da in ogni caso non e' un errore ma un NOTICE. Ti consiglio di togliere quel tipo di notice dal php.ini; li' dentro trovi una sezione tipo questa:
codice:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Error handling and logging ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; error_reporting is a bit-field. Or each number up to get desired error
; reporting level
; E_ALL - All errors and warnings
; E_ERROR - fatal run-time errors
; E_WARNING - run-time warnings (non-fatal errors)
; E_PARSE - compile-time parse errors
; E_NOTICE - run-time notices (these are warnings which often result
; from a bug in your code, but it's possible that it was
; intentional (e.g., using an uninitialized variable and
; relying on the fact it's automatically initialized to an
; empty string)
; E_CORE_ERROR - fatal errors that occur during PHP's initial startup
; E_CORE_WARNING - warnings (non-fatal errors) that occur during PHP's
; initial startup
; E_COMPILE_ERROR - fatal compile-time errors
; E_COMPILE_WARNING - compile-time warnings (non-fatal errors)
; E_USER_ERROR - user-generated error message
; E_USER_WARNING - user-generated warning message
; E_USER_NOTICE - user-generated notice message
;
; Examples:
;
; - Show all errors, except for notices
;