Ciao,

non ho mai usato MySQL ma ho trovato questo:

With both DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP clauses, the column has the current timestamp for its default value, and is automatically updated.
With neither DEFAULT nor ON UPDATE clauses, it is the same as DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP.
With a DEFAULT CURRENT_TIMESTAMP clause and no ON UPDATE clause, the column has the current timestamp for its default value but is not automatically updated.
With no DEFAULT clause and with an ON UPDATE CURRENT_TIMESTAMP clause, the column has a default of 0 and is automatically updated.
With a constant DEFAULT value and with ON UPDATE CURRENT_TIMESTAMP clause, the column has the given default and is automatically updated.


il link e'

http://dev.mysql.com/doc/mysql/en/TIMESTAMP_4.1.html

Saluti.
D.