The board or commission may issue a subpoena for the attendance of witnesses or the production of other evidence at a hearing upon the request of a member of the board or commission or upon the written demand of any party. The issuance and service of such subpoena shall be obtained upon the filing of an affidavit therefor which states the name and address of the proposed witness; specifies the exact things sought and states that the witness has the desired things in said witness' possession or under said witness' control. A subpoena need not be issued when the affidavit is defective in any particular. (2007 Code § 1-23)