On UPDATE Current_timestamp

CREATE TABLE time1 (
ID SMALLINT,
Time1 TIMESTAMP DEFAULT current_timestamp on UPDATE Current_timestamp,
Time2 TIMESTAMP DEFAULT Current_timestamp
) ;

INSERT into time1 VALUES (+, ', '), (101,now (), now ());

SELECT * from time1;

ID time1 time2
------  -------------------  ---------------------
0000-00-00 00:00:00 0000-00-00 00:00:00
101 2015-03-30 10:02:18 2015-03-30 10:02:18

UPDATE time1 SET id=102;

SELECT * from time1;

ID time1 time2
------  -------------------  ---------------------
102 2015-03-30 10:03:10 0000-00-00 00:00:00
102 2015-03-30 10:03:10 2015-03-30 10:02:18

Summarize:

The DEFAULT current_timestamp on update current_timestamp---can be used to record the last update time.

On UPDATE Current_timestamp