ANY_VALUE is treated as aggregation, so returns error in combination with aggregation functions

CREATE TABLE t (a INT);

INSERT INTO t VALUES (1),(2),(3);

SELECT SUM(ANY_VALUE(a)) FROM t;

SELECT ANY_VALUE(SUM(a)) FROM t;

SELECT COUNT(DISTINCT ANY_VALUE(a)) FROM t;

MariaDB [test]> SELECT SUM(ANY_VALUE(a)) FROM t;

ERROR 1111 (HY000): Invalid use of group function

MariaDB [test]> SELECT ANY_VALUE(SUM(a)) FROM t;

ERROR 1111 (HY000): Invalid use of group function

MariaDB [test]> SELECT COUNT(DISTINCT ANY_VALUE(a)) FROM t;

ERROR 1111 (HY000): Invalid use of group function