MySQL Bugs: #73290: Unnecessary set via CURRENT

Bug #73290	Unnecessary set via CURRENT_TIMESTAMP in transactions
Submitted:	14 Jul 2014 10:30
Reporter:	Marco Rossi	Email Updates:
Status:	Open	Impact on me:	None
Category:	MySQL Server: Data Types	Severity:	S4 (Feature request)
Version:	5.6	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
Unnecessary set via CURRENT_TIMESTAMP in transactions

How to repeat:
Let's say you have a row that is:

id | name | mtime
 1 | test | 2013-02-02 02:02:02

and mtime column has ON UPDATE CURRENT_TIMESTAMP.

I think in this transaction the mtime shouldn't be touched...

START TRANSACTION;
UPDATE mytable SET name = 'something' WHERE id = 1;
...
...
...
UPDATE mytable SET name = 'test' WHERE id = 1;
COMMIT;

...since the row wasn't actually modified at the time of the commit.

Just a cosmetic issue, don't know if makes sense, but I'd have expected the datetime value to remain unchanged since changes are made within a transaction.

Interesting idea, but would it really be worth the effort of tracking/caching all value changes throughout the lifetime of a transaction and compare changes against the list of already performed changes to identify possible "value change reverted later in transaction" situations just for this?

(with InnoDB extra storage/tracking may not be needed as UNDO records could be checked for this, but it would still be quite a bit of effort to check them for previous changes ...