Question

Is it possible to have a timestamp constraint in mysql that MUST come from the system and can not otherwise be provided in the insert or update query?

Is it possible to keep a table from being updated with a constraint? I understand how to keep a mysql user from updating a table with GRANT but in my case a constraint may be preferred as it is my goal to guarantee the timestamp of the record regardless of user including root.

Answer 1

What you can do is to overwrite the value on INSERT and UPDATE using a trigger

So no matter what the query sets, the value of your desired timestamp field will always be the system time.

DELIMITER ;;

CREATE TRIGGER before_yourtable_insert 
BEFORE INSERT ON yourtable
FOR EACH ROW
BEGIN
    SET NEW.datefield := CURRENT_TIMESTAMP;
END;;

CREATE TRIGGER before_yourtable_update 
BEFORE UPDATE ON yourtable
FOR EACH ROW
BEGIN
    SET NEW.datefield := CURRENT_TIMESTAMP;
END;;

DELIMITER ;

EDIT 1:
Just realized you actually wanted to prevent that the once set system time could be updated later.
Slightly modify your UPDATE trigger to have this job done.

SET NEW.datefield := OLD.datefield resets the value to the old value on each update

CREATE TRIGGER before_yourtable_update 
BEFORE UPDATE ON yourtable
FOR EACH ROW
BEGIN
    SET NEW.datefield := OLD.datefield;
END;;