MySQL UPDATE TIMESTAMP on row UPDATE, even when all other row data remains the same?

I have a table with a timestamp.

The timestamp is set to "ON UPDATE CURRENT_TIMESTAMP."

When I run an update on a row with data that is the same as the data already in that row, I still want the 开发者_如何学CTIMESTAMP to update. It does not. Why does it not? If the data is different it updates just fine.

I realize I can force an update with TIMESTAMP = now(), but I am trying to understand what MySQL is doing.

You have said ON UPDATE.

There is no update happening if all the row's values are the same.