here I prefer the 'relaxed parsing' in Maria DB.
CREATE TABLE `d` (
`rec_id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
`datetime` DATETIME(4) DEFAULT NULL,
`timestamp` TIMESTAMP(4) NOT NULL DEFAULT CURRENT_TIMESTAMP(5) ON UPDATE CURRENT_TIMESTAMP(4),
PRIMARY KEY (`rec_id`)
) ENGINE=INNODB;
-- it actually creates the table
SHOW CREATE TABLE d;
/* returns
CREATE TABLE `d` (
`rec_id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`datetime` datetime(4) DEFAULT NULL,
`timestamp` timestamp(4) NOT NULL DEFAULT CURRENT_TIMESTAMP(4) ON UPDATE CURRENT_TIMESTAMP(4),
PRIMARY KEY (`rec_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
*/
I don't think DEFAULT CURRENT_TIMESTAMP(5) should be accepted for the datatype DATETIME(4).