Can a defendant withdraw a previous not guilty plea?

Penal Code section 1017 is of no assistance; it merely provides pleas must be made in open court, orally or in writing. But section 1016 of the Penal Code sets out the six pleas which may be entered to a criminal charge; and the statute does not require the "approval of the court" for any plea other than nolo contendere and does not require a showing of good cause to amend any plea post-arraignment, except to add the defense of not guilty by reason of insanity. The Attorney General cites one case for the claim there is no automatic right to withdraw a previous not guilty plea (People v. Staples (1906) 149 Cal. 405, 409, 86 P. 886), but it held only that the court did not abuse its discretion in denying a motion to set aside a plea of not guilty in order to hear a motion to dismiss the indictment where the defendant made no showing of a good ground for the proposed motion.