The ISO/IEC 13249-3:2016 specifies a ST_NumInteriorRing() function, which uses a singular "Ring" word. A lot of RDBMS have rectified this flaw in the standard by offering an alias ST_NumInteriorRings(), and so does MariaDB:

SELECT

    st_numinteriorrings(st_geomfromtext('POLYGON (

      (-3 -3, 3 -3, 3 3, -3 3, -3 -3),

      (-2 -2, 2 -2, 2 2, -2 2, -2 -2), 

      (-1 -1, 1 -1, 1 1, -1 1, -1 -1)

    )', 0)) n

Unfortunately, st_numinteriorring() doesn't work. I suggest supporting both names, just like MySQL.