The HOUR SQL Function in MySQL and MariaDB - Hour of date or time

SELECT hour(now());
SELECT hour(adddate(now(), interval 1 hour));
SELECT hour(utc_timestamp());
SELECT hour('2022-03-29');
SELECT hour('2022-03-29 12:15:30');
SELECT hour(20210216);
SELECT hour(20210216121530);

SELECT hour('12:15:30');
SELECT hour('138:15:30');
SELECT hour(1381530);

SELECT hour('2022-03-29 138:15:30');
SELECT hour('0000-00-00 00:00:00');
SELECT hour(unix_timestamp());
SELECT hour('xxx');
SELECT hour(null);