如果不是真的需要在php中进行"，则可以使用MySQL的内置Trigger机制来进行此更新.

If doing it "in php" isn't really a requirement, then you can use MySQL's built in Trigger mechanism to do this update.

触发器在事件(插入，更新，删除)之后或之前导致某些事情发生

Triggers cause something to happen AFTER or BEFORE an event(INSERT, UPDATE,DELETE)

所以您的触发条件是:

CREATE TRIGGER thistrigger AFTER INSERT
ON User FOR EACH ROW
UPDATE PROFILE SET "whatever"

关于触发器: http://dev.mysql.com/doc/refman/5.0/en/create-trigger.html