MySQL is not allowing ON UPDATE CURRENT_TIMESTAMP for a DATETIME field

Question

I have seen a lot of related questions, but I cannot place my finger on this specific question:

I have a MySQL table with both a TIMESTAMP (for when the field was create

Answer 1

INSERT and UPDATE date/time automatically

Works with data type: DATETIME or TIMESTAMP

Tested on: MySQL 5.6.27-2 and MariaDB 10.1.10

---

Stores the current date and time on INSERT

CREATE TABLE table_demo (
    ...
    `CreatedAt` datetime DEFAULT CURRENT_TIMESTAMP
    ...
);

Stores the current date and time on INSERT and UPDATE

CREATE TABLE table_demo (
    ...
    `UpdatedAt` datetime DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
    ... 
);

Stores the current date and time only on UPDATE

NOTE: when INSERT, the default value is '0000-00-00 00:00:00'

CREATE TABLE table_demo (
    ...
    `UpdatedAt` datetime DEFAULT '0000-00-00 00:00:00' ON UPDATE CURRENT_TIMESTAMP
    ...
);