(a) No person offered as a witness shall be excluded by reason of incapacity, for crime or interest or from being a party, from giving evidence, either in person or by deposition, according to the practice of the court, on the trial of any issue joined, or of any matter or question, or on any inquiry arising in any suit, action, or proceeding, civil or criminal, in any court or before any judge, jury, sheriff, coroner, magistrate, officer, or party having by law or consent of parties authority to hear, receive, and examine evidence; but every person so offered shall be competent and compellable to give evidence on behalf of either or any of the parties to the suit, action, or other proceeding.

(b) This Code section, as revised by an Act approved April 17, 1979 (Ga. L. 1979, p. 1261), shall apply to transactions or occurrences which take place on or after July 1, 1979, and this Code section, as it existed prior to July 1, 1979, shall apply to transactions or occurrences which took place prior to July 1, 1979.