Who was over David's army?

Answer: Joab son of Zeruiah

Joab commanded the army, Jehoshaphat was recorder, Zadok and Ahimelech were priests, and Benaiah led the Cherethites and Pelethites.

“Joab son of Zeruiah was over the army; Jehoshaphat son of Ahilud was the recorder;”— 2 Samuel 8:16 (BSB)